ANATOMY

Detailed explanation-1: -At the start of the cycle, during ventricular diastole–early, the heart relaxes and expands while receiving blood into both ventricles through both atria; then, near the end of ventricular diastole–late, the two atria begin to contract (atrial systole), and each atrium pumps blood into the ventricle below it.

Detailed explanation-2: -The cardiac cycle begins with atrial systole, the sequential activation and contraction of the 2 thin-walled upper chambers. Atrial systole is followed by the delayed contraction of the more powerful lower chambers, termed ventricular systole.

Detailed explanation-3: -Diastole begins with the closing of the aortic valve (or pulmonic) and ends with the closing of the mitral valve (or tricuspid). This period encompasses the ventricular relaxation and filling. Diastole represents when the blood vessels return blood to the heart in preparation for the next ventricular contraction.

Detailed explanation-4: -The atrial systole, ventricular systole, atrial diastole, and ventricular diastole are clearly mentioned in the cardiac cycle diagram given below.

Detailed explanation-5: -Isovolumetric Relaxation-Occurs during early diastole. Occurs during mid to late diastole, when the heart chambers are relaxed. Blood flows passively into the atria, through open AV valves, and into the ventricles, where the pressure is lower. Atria contract, forcing the remaining blood into the ventricles.