Describe the Cardiac Cycle

The Cardiac Cycle can be split into three stages: Diastole, Atrial Systole, and Ventricular Systole. (Left side of heart used for example purposes). Atrial Systole: Blood enters the atrium via the pulmonary veins. The atrium contracts, atrial pressure (Ap) increases above that of ventricular pressure (Vp) opening the atrioventricular valve (AVV) , and forcing blood into the left ventricle.Ventricular Systole: The ventricle starts to contract. Vp increases above Ap, causing the AVV to close. Pressure further increases. Vp then increases above aortic pressure (AOp). This forces open the semilunar valve squeezing blood up and out of the ventricles into the aorta so it can travel around the body to respiring tissues. Diastole is when all the heart muscles are relaxed. Vp decreases below AOp so the semilunar closes (retrograde movement of blood). Passive filling of atria.