Zoology - Body Fluids and Circulation Question with Solution | TestHub

Contraction of heart chambers is called systole and
relaxation is called diastole. Atria and ventricles contract alternately.

Right atrium receives deoxygenated blood and left atrium receives oxygenated blood. When both the atria are completely filled with blood, pressure is exerted on the wall due to which SA node gets excited and generates cardiac impulse. This leads to atrial systole. During atrial systole, blood is pumped into ventricles.

The opening between the right atrium and the right ventricle is guarded by the tricuspid valve, whereas a bicuspid valve guards the opening between the left atrium and the left ventricle.

So, during atrial systole, the bicuspid and tricuspid valves are open, and the pulmonary/aortic semilunar valves are closed.