Name: heartbeat stages and valve action
Uploaded: 2025-05-15T09:13:32.000Z
Duration: 1 min 29 s
Channel: JoVE

K12 Standards

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

9-12

Human Anatomy and Physiology

Transport

Cardiovascular System

Cardiac Cycle

The cardiac cycle comprises the contraction, or systole, and relaxation, or diastole, during one heartbeat.
During atrial systole, cardiac action potential from the sinoatrial node triggers atrial contraction, ejecting blood into the ventricles, following which the atria enter diastole.
At the end of ventricular diastole, the ventricles contain about 130 mL of blood, called the end-diastolic volume.
The cardiac potential traveling down the atrioventricular node triggers ventricular systole.
As the ventricles contract, the rising pressure closes the atrioventricular valves. This phase is called isovolumetric contraction, where all valves remain closed, maintaining a constant ventricular blood volume.
Eventually, ventricular pressure exceeds arterial pressure, prompting the semilunar valves to open and eject blood. The leftover blood, about 60 mL, called the end-systolic volume, stays in the ventricles.
During ventricular diastole,&#160; repolarization reduces the pressure, triggering arterial backflow, closing the semilunar valves, and leading to isovolumetric relaxation of the ventricles.
While the ventricles were contracting, the atria were being filled with blood. Eventually, the atri

cardiac cycle

The cardiac cycle refers to the sequence of events that occur in the heart from the beginning of one heartbeat to the next. It's characterized by alternating periods of contraction (systole) and relaxation (diastole) of the heart muscles.
During the cardiac cycle, blood flow through the heart is regulated entirely by changing pressure gradients. This sequence of events begins with the heart in a state of total relaxation, known as mid-to-late diastole, during which blood passively flows from the atria into the ventricles.
The contraction of the atria marks the onset of atrial systole, pushing the remaining blood into the ventricles. Following this, the ventricles initiate their contraction process, a phase referred to as isovolumetric contraction, as both the atrioventricular and the semilunar valves are closed, maintaining a constant volume of blood inside the ventricles. Shortly after this, the pressure inside the ventricles leads to the opening of the semilunar valves, facilitating the ejection of blood into the aorta and pulmonary trunk.
After the ejection phase, the ventricles return to a relaxed state, a phase known as early diastole or isovolumetric relaxation, as all four valves are closed. The closing of the aortic valve briefly increases pressure inside the aorta, an event marked by the dicrotic notch on the pressure graph.
Meanwhile, the atria have been filling up with blood throughout this ventricular systole, thereby preparing for the next cycle.
The cardiac cycle lasts approximately 0.8 seconds in an average heart that beats around 75 times per minute. Atrial systole accounts for 0.1 seconds, ventricular systole for 0.3 seconds, and total heart relaxation for the remaining 0.4 seconds.
The right and left sides of the heart function in synchrony but differ in pressure due to the less demanding pulmonary circulation. As a result, the right ventricular walls are thinner than the left. Regardless of this difference in pressure, both sides of the heart eject an equal volume of blood with each heartbeat.

The cardiac cycle comprises the contraction, or systole, and relaxation, or diastole, during one heartbeat.
During atrial systole, cardiac action ...

Education

JoVE Core

Anatomy and Physiology

Unit 1

The Heart

KEY TERMS AND CONCEPTS

heartbeat stages and valve action

The heartbeat follows a set of stages that move blood through the heart. This process is driven by changes in pressure and by the opening and closing of the heart valves. It includes systole, or contraction, and diastole, or relaxation.

The sequence starts in mid-to-late diastole, when the heart is fully relaxed. During this time, blood flows passively from the atria into the ventricles. Atrial systole then begins as the atria contract and push the remaining blood into the ventricles.

Next comes ventricular contraction, called isovolumetric contraction. At this point, both the atrioventricular valves and the semilunar valves are closed, so the blood volume in the ventricles stays constant. As ventricular pressure rises, the semilunar valves open and blood is ejected into the aorta and pulmonary trunk.

After ejection, the ventricles relax again in early diastole, also called isovolumetric relaxation. All four valves are closed during this phase. The closing of the aortic valve briefly raises pressure in the aorta, which is seen as the dicrotic notch on a pressure graph. While the ventricles cycle through these stages, the atria keep filling with blood and prepare for the next beat.

An average heart that beats about 75 times per minute completes one cardiac cycle in around 0.8 seconds. Atrial systole lasts about 0.1 seconds, ventricular systole lasts about 0.3 seconds, and the remaining 0.4 seconds are spent in total heart relaxation. The right and left sides of the heart work together, but they face different pressure demands because pulmonary circulation is less demanding. That is why the right ventricular walls are thinner than the left, even though both sides eject the same volume of blood with each heartbeat.

Heartbeat Stages and Valve Action

overview of the heart

How the Heart Pumps Blood

The heart is a muscular organ in the chest that pumps blood through the body. It works as the main pump of the vascular system. The heart has four chambers. The two atria are on top, and the two ventricles are below. Blood enters the right atrium from the body as deoxygenated blood, which means it has less oxygen. It then moves to the right ventricle. The right ventricle pumps this blood to the lungs for oxygenation. Oxygenated blood returns from the lungs to the left atrium. It then passes to...

location and orientation of the heart

Heart Position, Apex, and Pericardium

The human heart sits in the mediastinum, the middle space of the thorax. It is about the size of a fist and weighs about 250 to 350 grams. The heart lies on the superior surface of the diaphragm and extends obliquely for about 12 to 14 cm. The heart is positioned anterior to the vertebral column and posterior to the sternum. About two-thirds of its mass lies to the left of the midsternal line. The lungs lie on either side of the heart. The broad base of the heart points toward the right...

layers of the heart wall

Heart Wall Layers and Their Roles

The heart wall has three layers: the epicardium, myocardium, and endocardium. Each layer has a different structure and job. Together, they help the heart pump blood through the body. The outermost layer is the epicardium. It is the visceral layer of the serous pericardium. This layer has a thin, transparent mesothelial surface and an inner layer of areolar connective tissue. Fat deposits are also found here, and they increase with age. The myocardium is the thickest layer of the heart wall.

chambers of the heart

Heart Chambers and Blood Flow Pathway

The heart chambers work together to move blood through the body and the lungs. The human heart has four chambers: the right atrium, right ventricle, left atrium, and left ventricle. The atria are the upper chambers, and the ventricles are the lower chambers. They are separated by the interatrial septum and the interventricular septum. The outside of the heart also shows clear dividing lines. The coronary sulcus separates the atria from the ventricles. The anterior and posterior...

heart valves

How Heart Valves Prevent Backflow

The heart valves keep blood moving in one direction through the heart. The main valve groups are the atrioventricular, or AV, valves and the semilunar valves. Together, they help stop blood from flowing backward as the heart chambers contract and relax. The AV valves stop blood from moving back into the atria when the ventricles contract. They work with the chordae tendineae, which are tough cord-like strands, and the papillary muscles. When the ventricles relax, the chordae tendineae are...

overview of systemic and pulmonary circulation

overview-of-systemic-and-pulmonary-circulation

Pathway of Blood Through Heart and Lungs

The circulatory system moves blood in two linked routes: pulmonary circulation and systemic circulation. Together, these circuits carry blood between the heart, the lungs, and the rest of the body. Pulmonary circulation comes first in this cycle. In pulmonary circulation, deoxygenated blood is pumped from the right ventricle to the lungs through the pulmonary trunk and pulmonary arteries. In the lungs, the blood picks up oxygen. It then returns to the heart through the pulmonary veins and...

coronary circulation

How the Heart Gets Its Blood

Coronary circulation is the blood supply that keeps the heart muscle alive. The heart does not use the same blood it pumps to feed itself. Instead, it depends on a separate vessel network that delivers oxygen and nutrients to the myocardium, or heart muscle. This is the shortest circulation in the body. Coronary circulation begins at the base of the aorta, where the left and right coronary arteries arise. These arteries wrap around the heart in the coronary sulcus and send blood inward to the...

conduction system of the heart

How the Heart Sets Its Own Beat

The heart sets its own beat through autorhythmicity, which is its built-in ability to generate electrical signals and start muscle contractions. This process depends on a self-regulating conduction system. It includes pacemaker cells and specialized conducting cells. Pacemaker cells are found in two main nodes: the sinoatrial (SA) node and the atrioventricular (AV) node. The SA node can depolarize on its own. That electrical change starts an action potential that causes the atria to contract. <br...

electrocardiogram

Reading Heart Waves on an ECG

An electrocardiogram, or ECG/EKG, records the heart’s electrical signals during each heartbeat. Electrodes are placed on the arms, legs, and chest. The electrocardiograph then amplifies the signals and creates 12 tracings that show the heart’s electrical activity from different views. A normal ECG has three main waveforms. The P wave shows atrial depolarization, which is the spread of action potentials through the atria. The QRS complex shows rapid ventricular depolarization, and the T wave...

The heartbeat follows a set of stages that move blood through the heart. This process is driven by changes in pressure and by the opening and closing of the heart valves. It includes systole, or contraction, and diastole, or relaxation. The sequence starts in mid-to-late diastole, when the heart is fully relaxed. During this time, blood flows passively from the atria into the ventricles. Atrial systole then begins as the atria contract and push the remaining blood into the ventricles. Next...

correlation between ecg and cardiac cycle

correlation-between-ecg-and-cardiac-cycle

ECG Waves Across the Cardiac Cycle

ECG waves show how the heart’s electrical signals line up with the cardiac cycle. The electrical activity appears before the heart muscle’s mechanical contraction and relaxation. On an electrocardiogram, the main waves help link each electrical event to a specific stage of the heartbeat. A cardiac action potential starts in the SA node, or sinoatrial node, and spreads through the atria and the AV node in about 0.03 seconds. This creates the P wave on the ECG and triggers atrial contraction.

disturbances in heart rhythm

Heart Rhythm Disorders and Emergency Care

Heart rhythm disorders, also called arrhythmias or dysrhythmias, happen when the heart’s conduction system has a defect. They can make the heart beat irregularly, too fast, or too slow. People may notice chest pain, shortness of breath, or fainting. Many things can trigger an arrhythmia. Stress, caffeine, alcohol, nicotine, cocaine, certain drugs, congenital defects, diseases, and electrolyte imbalances are all possible causes. These triggers can disrupt the electrical signals that control the...

heart sounds

Auscultation and Normal Heart Sounds

Auscultation is the process of listening to internal body sounds with a stethoscope. Heart sounds are created by turbulence in blood flow when the heart valves close. These sounds are usually heard best a little away from the valves, where the blood flow spreads the sound. The heart makes four types of sounds, but a stethoscope usually picks up only S1 and S2. S1 is the “lub” sound. It happens when the atrioventricular, or A-V, valves close at the start of ventricular systole. S1 is usually...

cardiac output and stroke volume

How Heart Rate Shapes Cardiac Output

Cardiac output shows how much blood the heart pumps each minute. It is the volume ejected by the left or right ventricle into the aorta or pulmonary trunk. Heart rate and stroke volume work together to set this value. Heart rate is the number of heartbeats per minute, and stroke volume is the amount of blood pumped out with each beat. Cardiac output is found by multiplying heart rate by stroke volume. In an average resting adult male, it is about 5.25 L/min. That estimate uses a heart rate of...

regulation of stroke volume

Stroke Volume: Preload to Afterload

Stroke volume depends on preload, contractility, and afterload. These three factors work together to control how much blood a ventricle ejects with each heartbeat. Understanding them helps explain how the heart keeps blood moving through the circulatory system. Preload is the stretch on the heart before it contracts. It is linked to the Frank-Starling law of the heart, which says that when the heart fills with more blood during diastole, it contracts more forcefully during systole. Preload is...

regulation of heart rates

How the Heart Adjusts Its Beat

Heart rate changes through signals from the autonomic nervous system, hormones, and the heart's own built-in control systems. The autonomic nervous system has two main parts. The sympathetic nervous system raises heart rate, and the parasympathetic nervous system lowers it. The sympathetic nervous system releases norepinephrine and epinephrine. These chemicals act on beta-1 adrenergic receptors in the heart. They increase the rate of depolarization in the sinoatrial (SA) node, which is the...

exercise and cardiac output

How Exercise Strengthens the Heart

Exercise strengthens the heart and improves cardiovascular health. Aerobic exercise is especially effective. The American Heart Association recommends 150 minutes of moderate to intense aerobic exercise each week for a healthy heart. Brisk walking, running, bicycling, cross-country skiing, and swimming are all examples. These activities are best done three to five times per week. During sustained exercise, muscles need more oxygen. The body meets this demand through enough cardiac output and...

imbalances in cardiac output

Congestive Heart Failure Causes and Effects

Congestive heart failure (CHF) happens when the heart becomes an inefficient pump. The heart normally keeps blood leaving the heart and blood returning to it in balance. When that balance is disrupted, blood circulation drops and the body does not get enough flow. CHF can affect the left side of the heart, the right side, or both. Left-side failure can cause pulmonary congestion, which means blood backs up in the lungs. The right side may still send blood to the lungs, but the left side cannot...

development of the heart

Heart Tube Formation and Folding

Heart tube formation and folding shape the early human heart. The process begins in the mesoderm, a middle layer of embryonic tissue, on day 18 or 19 after fertilization. It starts in the cardiogenic area, a group of mesodermal cells at the head end of the embryo. These cells extend into cardiogenic cords and then change into hollow endocardial tubes. As the embryo folds from side to side, the paired tubes move closer together. They join into one primitive heart tube by day 21. By day 22, this...

key terms and concepts

Trace the stages of one heartbeat, from filling and atrial systole to ventricular ejection, valve closure, and relaxation in the cardiac cycle.

Heartbeat Stages and Valve Action | JoVE K12

anatomy and physiology

JoVE Core Anatomy and Physiology showcases the anatomical and physiological details of the human body in comprehensive, clear, and engaging video animations. This collection of lessons focuses on the structures, components, functions, and requirements of the human body. It is complemented by scientist-in-action videos that demonstrate the application of this knowledge in real-world medical and research settings.

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The cardiovascular or circulatory system comprises the blood, the heart, and the blood vessels.
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extrinsic-and-intrinsic-pathways-of-hemostasis

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Rh Blood Group

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Blood

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Blood

Overview of the Heart

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It is cone-shaped and weighs about 250 to 300 grams on average.
The heart is ...

Location and Orientation of the Heart

The heart is located in the mediastinum and spans from the first rib to the diaphragm. It lies anterior to the vertebral column, posterior to the sternum, ...

Layers of the Heart Wall

The heart wall has three layers&#8212;the epicardium, the myocardium, and the endocardium.
The outermost layer, the epicardium, is the visceral layer of ...

Chambers of the Heart

The heart has four chambers&#8212;the right atrium, right ventricle, left atrium, and left ventricle.
Externally, the coronary sulcus separates the atria ...

Heart Valves

The heart valves open and close in response to the pressure gradients created by the contracting heart chambers.
These valves regulate the blood flow by ...

Overview of Systemic and Pulmonary Circulation

The pulmonary and systemic circuits work sequentially to move blood between the heart, lungs, and peripheral tissues.
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Coronary Circulation

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Conduction System of the Heart

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Electrocardiogram

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Correlation between ECG and Cardiac Cycle

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Disturbances in Heart Rhythm

Disturbances in the heart rhythm, or arrhythmia, can cause irregular heartbeats.
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Heart Sounds

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Cardiac Output and Stroke Volume

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Regulation of Stroke Volume

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Regulation of Heart Rates

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Exercise and Cardiac Output

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Imbalances in Cardiac Output

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Development of the Heart

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Venous Return

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Venules

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Cardiovascular System

Content elaboration: The cardiovascular system consists of the heart and blood vessels. The heart is mostly comprised of cardiac muscle which is supplied with oxygenated blood by coronary arteries. The structure of the heart includes four chambers, four valves and major vessels leading to and from the heart. The flow of blood through the heart, pulmonary and systemic circuits should be explored. Blood flows from arteries, to arterioles, to capillaries, to venules, then to veins. In the capillaries, oxygen, nutrients, and chemical messengers diffuse out (leave) and carbon dioxide and other waste products diffuse in (enter). Veins have valves that keep the blood flowing toward the heart. The primary function of the cardiovascular system is the transport of oxygen, carbon dioxide, hormones, nutrients, waste products and chemical messengers. Processes involved in the cardiovascular system include the cardiac cycle and cardiac and conductive pathway which is measured by electrocardiograms and blood pressure. Homeostatic imbalances are explored. These include, but are not limited to, a variety of cardiovascular diseases and structural imperfections of the heart, valves and vessels. Examples include, but are not limited to, myocardial infarction, aneurysm, atherosclerosis, hypertrophic cardiomyopathy, hypo/hypertension and arrhythmias. Investigations are used to understand and explain the cardiovascular system in a variety of inquiry and design scenarios that can incorporate evolutionary concepts, scientific reasoning, comparative analysis, communication skills and real-world applications.

Heartbeat Stages and Valve Action

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