For more videos please visit: http://www.meritnation.com Have you heard your heart beat? What is the sound like? Yes, it sounds like ‘lubb-dubb’, ‘lubb-dubb’! This sound is produced when the heart produces a pressure when it beats. Now, what causes the beating of the heart? The sequence of events that take place during a single heart beat is known as the Cardiac Cycle. It is not so simple. It is a complex process which involves a sequence of activities and that too within 0.8 sec. The cardiac cycle consists of a systole and a diastole. The cardiac cycle begins with a joint diastole (relaxation of all four chambers of the heart). This is followed by an arterial systole (contraction of left and right atria) stimulated by the generation of an action potential by the Sino-Auricular Node (SA node). As a result of the arterial systole, the blood from the atria drains into the ventricles. The impulse produced by the SA Node is then picked up by the Atrio-Ventricular Node (AV node) and is conducted throughout the ventricles leading to the ventricular systole. During the ventricular systole, the blood from the ventricles is drained into the aorta and the pulmonary artery. This is followed by closing of the AV valves which produces the sound ‘lubb’ and the closure of the Semilunar valves causes produces the sound ‘dub’. How your heart works – Know your cardiac cycle and blood flow in heart.