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The purpose of our heart is to pump blood throughout our body; it does it in a repeating sequence called the cardiac cycle. The car diac cycle is the coordination of the filling and emptying of the heart of blood by electrical signals that cause the heart muscles to contract and relax. The cardiac cycle is essentially split into two phases, systole (the contraction phase) and diastole (the relaxation phase).

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PHASES OF THE CARDIAC CYCLE
Atriole systole
begins
Atrial contraction
forces blood into
ventricles
p
P -Wave
Atria depolarization
Ventricular systole
(first phase)
Ventricular
contraction pushes
A V valves closed
QRS Complex
Ventricle depolarization
Ventricular systole
(second phase)
Semilunar valves
open and blood
T - Wave
Ventricular diastole
(early)
Semilunar valves
Ventricular diastole
(late)
S
Atrial
Diastole
Atrial
Systole
Ventricular repolarization
Atrial Diastole
Ventricular Diastole
Ventricular Systole
Ventricular Diastole

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Atriole systole
begins
Atrial contraction
forces blood into
ventricles

Atrial systole -  During atrial systole, the left and right atria contract at the same time and push blood into the left and right ventricle Lasts about 0.1 seconds

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Ventricular systole
(first phase)
Ventricular
contraction pushes
AV valves closed

Ventricular systole (first phase)/ Isovolumic contraction -  The isovolumetric contraction causes left ventricular pressure to rise above atrial pressure, which closes the mitral valve and produces the first heart sound.

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Ventricular systole
(second phase)
Semilunar valves
open and blood
is ejected

Ventricular Systole -   refers to the phase of the car diac cycle where the left and right ventricles contract at the same time and pump blood into the aorta and pulmonary trunk, respectively. The ventricular systole lasts about 0.3 seconds

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Ventricular diastole
(early)
Semilunar valves
close and blood
flows into atria

Ventricular diastole (early) -  The heart relaxes an d expands while receiving blood into both ventricles through both atria.

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Ventricular diastole
(late)
Chambers relax
and blood fills
ventricles passively

Ventricular diastole (late) -  as  the ventricular muscle relaxes, pressure on the blood within the ventricles drops even further. Eventually, it drops below the pressure in the atria. The ventricular diastole lasts approximately 430 ms.

how does the human heart work

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