Explanation: there are two processes that takes place in cardiac cycle. These procesesss comprises of complete relaxation and contraction of both the atria and ventricles which usually last for about 0.8 seconds. Starting with the chambers in the diastole, blood flows passively from the veins into the atria and past the atrioventicular valves into the ventricles. Contraction begins in the atria following the depolarization of the atria and blood is pumped into the ventricles. The ventricles begins contraction by raising pressure within the ventricles.
A. depolarization of the atria and pump blood into the ventricles.
Explanation:
Contraction of atria is also called atrial systole which is responsible for the pumping of blood into the ventricles. The blood moves from the atria into the ventricles, opening the atrioventricular valves and completed one heart cycle. Contraction of ventricle is known as ventricle systole. During contraction of ventricle, blood is transported to two regions, one is the lung for cleaning and other is all parts of the body.
