Cardiac cycle

heartbeatheart beatventricular systoleatrial systolebeatingheart contractionheartbeatssystolic heartbeatbeating of the heart
The cardiac cycle is the performance of the human heart from the ending of one heartbeat to the beginning of the next.wikipedia
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Diastole

diastolicdiastolic pressurerelaxation
It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, followed by a period of robust contraction and pumping of blood, dubbed systole.
Diastole is the part of the cardiac cycle during which the heart refills with blood after the emptying done during systole (contraction).

Systole

systolicsystolic pressureventricular systole
It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, followed by a period of robust contraction and pumping of blood, dubbed systole.
The systole is the part of the cardiac cycle during which some chambers of the heart muscle contract after refilling with blood.

Ejection fraction

left ventricular ejection fractionLVEFejected
Due to the contractions of the systole, pressures in the ventricles rise quickly, exceeding the pressures in the trunks of the aorta and the pulmonary arteries and causing the requisite valves (the aortic and pulmonary valves) to open—which results in separated blood volumes being ejected from the two ventricles.
An ejection fraction (EF) is the volumetric fraction (or portion of the total) of fluid (usually blood) ejected from a chamber (usually the heart) with each contraction (or heartbeat).

Tricuspid valve

tricuspidtricuspid valvesheart
The mitral and tricuspid valves, also known as the atrioventricular, or AV valves, open during ventricular diastole to permit filling.
The tricuspid valve functions as a one-way valve that closes during ventricular systole to prevent regurgitation of blood from the right ventricle back into the right atrium.

Blood pressure

systolic blood pressurediastolic blood pressurearterial blood pressure
Throughout the cardiac cycle, blood pressure increases and decreases.
Blood pressure is usually expressed in terms of the systolic pressure (maximum during one heartbeat) over diastolic pressure (minimum in between two heartbeats) and is measured in millimeters of mercury (mmHg), above the surrounding atmospheric pressure.

Wiggers diagram

After ventricular pressures fall below their peak(s) and below those in the trunks of the aorta and pulmonary arteries, the aortic and pulmonary valves close again—see, at right margin, Wiggers diagram, blue-line tracing.
The Wiggers diagram clearly illustrates the coordinated variation of these values as the heart beats, assisting one in understanding the entire cardiac cycle.

Heart rate

heartbeatresting heart ratemaximum heart rate
Cardiac muscle is composed of myocytes which initiate their internal contractions without applying to external nerves—with the exception of changes in the heart rate due to metabolic demand.
Heart rate is the speed of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm).

Mitral valve

mitralbicuspid valvemitral annulus
The mitral and tricuspid valves, also known as the atrioventricular, or AV valves, open during ventricular diastole to permit filling.
The mitral annulus is saddle shaped and changes in shape throughout the cardiac cycle.

Ventricle (heart)

ventricleleft ventricleright ventricle
There are two atrial and two ventricle chambers of the heart; they are paired as the left heart and the right heart—that is, the left atrium with the left ventricle, the right atrium with the right ventricle—and they work in concert to repeat the cardiac cycle continuously, (see cycle diagram at right margin). The upper two chambers, the left and right atria, are entry points into the heart for blood-flow returning from the circulatory system, while the two lower chambers, the left and right ventricles, perform the contractions that eject the blood from the heart to flow through the circulatory system.
During most of the cardiac cycle, ventricular pressure is less than the pressure in the aorta, but during systole, the ventricular pressure rapidly increases, and the two pressures become equal to each other (represented by the junction of the blue and red lines on the diagram on this page), the aortic valve opens, and blood is pumped to the body.

Electrocardiography

electrocardiogramECGEKG
In an electrocardiogram, electrical systole initiates the atrial systole at the P wave deflection of a steady signal; and it starts contractions (systole).
In this way, the overall magnitude and direction of the heart's electrical depolarization is captured at each moment throughout the cardiac cycle.

Aorta

aorticaortic archaortic root
Due to the contractions of the systole, pressures in the ventricles rise quickly, exceeding the pressures in the trunks of the aorta and the pulmonary arteries and causing the requisite valves (the aortic and pulmonary valves) to open—which results in separated blood volumes being ejected from the two ventricles.
These return waves create the dicrotic notch displayed in the aortic pressure curve during the cardiac cycle as these reflected waves push on the aortic semilunar valve.

Heart

cardiachuman heartapex of the heart
There are two atrial and two ventricle chambers of the heart; they are paired as the left heart and the right heart—that is, the left atrium with the left ventricle, the right atrium with the right ventricle—and they work in concert to repeat the cardiac cycle continuously, (see cycle diagram at right margin). The cardiac cycle is the performance of the human heart from the ending of one heartbeat to the beginning of the next.
The cardiac cycle refers to the sequence of events in which the heart contracts and relaxes with every heartbeat.

Atrial fibrillation

atrial fibrilationparoxysmal atrial fibrillationAtrial fibrillation with rapid ventricular response
Atrial kick is absent or disrupted if there is loss of normal electrical conduction in the heart, such as caused by atrial fibrillation, atrial flutter, or heart block.
Often it starts as brief periods of abnormal beating which become longer and possibly constant over time.

Circulatory system

cardiovascularcirculationcardiovascular system
The upper two chambers, the left and right atria, are entry points into the heart for blood-flow returning from the circulatory system, while the two lower chambers, the left and right ventricles, perform the contractions that eject the blood from the heart to flow through the circulatory system.
Back flow of blood through its opening during atrial systole is prevented by Thebesian valve.

Heart block

blockheart-blockSinoatrial heart block
Atrial kick is absent or disrupted if there is loss of normal electrical conduction in the heart, such as caused by atrial fibrillation, atrial flutter, or heart block.
The human heart uses electrical signals to maintain and initiate the regular heartbeat in a living person; incorrect conduction or interference from external sources can lead to mild or serious symptoms depending upon the location of the blockage and how severely conduction is being blocked.

Bundle of His

crus of heartHis bundle
Impulses of the wave are delayed upon reaching the AV node, which acts as a gate to slow and to coordinate the electrical current before it is conducted below the atria and through the circuits known as the bundle of His and the Purkinje fibers—all which stimulate contractions of both ventricles.
The fascicular branches then lead to the Purkinje fibers, which provide electrical conduction to the ventricles, causing the cardiac muscle of the ventricles to contract at a paced interval.

Cardiac output

Cardiac inputoutputoutput of the heart
The area under the flow-versus-time curve for one cardiac cycle is the stroke volume.

Atrium (heart)

right atriumatrialeft atrium
There are two atrial and two ventricle chambers of the heart; they are paired as the left heart and the right heart—that is, the left atrium with the left ventricle, the right atrium with the right ventricle—and they work in concert to repeat the cardiac cycle continuously, (see cycle diagram at right margin). The upper two chambers, the left and right atria, are entry points into the heart for blood-flow returning from the circulatory system, while the two lower chambers, the left and right ventricles, perform the contractions that eject the blood from the heart to flow through the circulatory system. Now follows the isovolumic relaxation, during which pressure within the ventricles begin to fall significantly, and thereafter the atria begin refilling as blood returns to flow into the right atrium (from the vena cavae) and into the left atrium (from the pulmonary veins).

Heart valve

heart valvesvalvesatrioventricular valves
The mitral and tricuspid valves, also known as the atrioventricular, or AV valves, open during ventricular diastole to permit filling.

Aortic valve

aorticaortic valvesaortic semilunar valve
Due to the contractions of the systole, pressures in the ventricles rise quickly, exceeding the pressures in the trunks of the aorta and the pulmonary arteries and causing the requisite valves (the aortic and pulmonary valves) to open—which results in separated blood volumes being ejected from the two ventricles.

Venae cavae

vena cavavena cavaevenæ cavæ
Now follows the isovolumic relaxation, during which pressure within the ventricles begin to fall significantly, and thereafter the atria begin refilling as blood returns to flow into the right atrium (from the vena cavae) and into the left atrium (from the pulmonary veins).

Pulmonary vein

pulmonary veinspulmonaryPulmonary venous
Now follows the isovolumic relaxation, during which pressure within the ventricles begin to fall significantly, and thereafter the atria begin refilling as blood returns to flow into the right atrium (from the vena cavae) and into the left atrium (from the pulmonary veins).

Cardiac pacemaker

pacemakerpacemaker cellscardiac pacemakers
The movements of cardiac muscle are coordinated by a series of electrical impulses produced by specialised pacemaker cells found within the sinoatrial node and the atrioventricular node.

Atrioventricular node

AV nodeatrioventricularAV
The movements of cardiac muscle are coordinated by a series of electrical impulses produced by specialised pacemaker cells found within the sinoatrial node and the atrioventricular node.

Myocyte

muscle fibermuscle cellmuscle cells
Cardiac muscle is composed of myocytes which initiate their internal contractions without applying to external nerves—with the exception of changes in the heart rate due to metabolic demand.