Cardiac cycle


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Cardiac cycle

Cardiovascular system

Anatomy and physiology

Cardiovascular system anatomy and physiology

Lymphatic system anatomy and physiology

Coronary circulation


Blood pressure, blood flow, and resistance

Pressures in the cardiovascular system

Laminar flow and Reynolds number

Resistance to blood flow

Compliance of blood vessels

Control of blood flow circulation

Microcirculation and Starling forces

Cardiac output

Measuring cardiac output (Fick principle)

Stroke volume, ejection fraction, and cardiac output

Cardiac contractility

Frank-Starling relationship

Cardiac preload

Cardiac afterload

Law of Laplace

Cardiac and vascular function curves

Altering cardiac and vascular function curves

Cardiac cycle and pressure-volume loops

Cardiac cycle

Cardiac work

Pressure-volume loops

Changes in pressure-volume loops

Cardiovascular physiological responses

Physiological changes during exercise

Cardiovascular changes during hemorrhage

Cardiovascular changes during postural change

Auscultation of the heart

Normal heart sounds

Abnormal heart sounds

Myocyte electrophysiology

Action potentials in myocytes

Action potentials in pacemaker cells

Excitability and refractory periods

Cardiac excitation-contraction coupling


Electrical conduction in the heart

Cardiac conduction velocity

ECG basics

ECG normal sinus rhythm

ECG intervals

ECG QRS transition

ECG axis

ECG rate and rhythm

ECG cardiac infarction and ischemia

ECG cardiac hypertrophy and enlargement

Blood pressure regulation



Renin-angiotensin-aldosterone system


Cardiac cycle


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Cardiac cycle

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External References

First Aid








Aortic valve

cardiac cycle p. 294

Cardiac cycle p. 294


cardiac cycle p. 294

Heart sounds p. 294

cardiac cycle p. 294

Mitral valve

in cardiac cycle p. 294

Rapid filling (cardiac cycle) p. 295


cardiac cycle p. 294

External Links



Rachel Yancey

Megan Gullotto, MSMI

Victoria Cumberbatch

Filip Vasiljević, MD

A cardiac cycle is the sequence of mechanical and electrical events that occurs with every heartbeat. Now, the heart is shaped like a cone and it contains two upper chambers, called atria; and two lower chambers, called ventricles.

Now, the left atrium receives oxygenated blood from the lungs via the pulmonary veins; while the right atrium receives deoxygenated blood from all of our organs and tissues via the superior and inferior vena cava.

From the atria, the blood flows into the lower chambers of the heart: the left ventricle, which pumps oxygenated blood to all our organs and tissues via the aorta; and the right ventricle, which pumps the deoxygenated blood back to the lungs via the pulmonary arteries.

Alright, so each heartbeat consists of two phases: systole, which is when the heart contracts and pumps blood out of the ventricles; and diastole, which is when the heart relaxes and ventricles fill with blood. Now, the cardiac cycle graph is used to express events during one cardiac cycle.

Along the y-axis are aortic pressure, left atrial pressure, and left ventricular pressure, heart sounds, ventricular volume, right atrial pressure curve, and ECG; while along the x-axis is time.

But, before we continue, here’s something to keep in mind: since there are no valves separating the right atrium from the superior vena cava and the jugular veins, the jugular venous pulse will follow the same pressure changes as the ones that arise in the right atrium.

In other words, an increase in the atrial pressure will result in an increased jugular venous pulse, and vice versa. Therefore, below the right atrial pressure curve let’s write JVP for jugular venous pulse.


The cardiac cycle is a repeating process by which the heart pumps blood into circulation. It consists of two phases: the diastole (relaxation) phase and the systole (contraction) phase.

During diastole, major events include isovolumetric ventricular relaxation and ventricular filling, which enables the heart to relax and ventricles to get filled with blood. During systole, the main events are isovolumetric ventricular contraction and systolic ejection, meaning the heart contracts and pumps the blood out of the ventricles.


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