ANATOMY

Detailed explanation-1: -The heart contracts twice for every heartbeat. One contraction is the atrial contraction while the other is the ventricular contraction.

Detailed explanation-2: -Ventricular systole commences with the closure of the mitral and tricuspid valves once ventricular pressure exceeds atrial pressure.

Detailed explanation-3: -The atria begin to contract (atrial systole), following depolarization of the atria, and pump blood into the ventricles. The ventricles begin to contract (ventricular systole), raising pressure within the ventricles.

Detailed explanation-4: -The cardiac cycle is defined as a sequence of alternating contraction and relaxation of the atria and ventricles in order to pump blood throughout the body. It starts at the beginning of one heartbeat and ends at the beginning of another.