Zoology - Body Fluids and Circulation Question with Solution | TestHub

Cardiac cycle has three stages:$1)$Joint diastole: In this all the four chambers are relaxed and thus AV valves are open while semilunar are closed.$2)$Atrial systole: Atria contract and AV valves are open.$3)$Ventricular systole: Ventricles contract and thus semilunar valves open and AV close. Thus never both AV and semilunar are open. The pressure in left atrium exceeds that of left ventricle throughout the ventricle ejection period. First heart sound is LUB due to closure of AV valves and second heart sound is DUB due to closure of semilunar valves.