In humans, blood passes from the post caval to the diastolic right...

The action of heart includes contractions and relaxations of the atria and ventricles. Contraction of the heart is called systole and relaxation is called diastole. The dynamics of blood flow in blood vessels is no exception and blood flows through the blood vessels along a pressure gradient, always moving from higher to lower pressure areas. Fundamentaly, the pumping action of heart generates blood flow. The contraction of atria is initiated and activated by sinoatrial node (SA node-Pacemaker), which spreads waves of contraction across the wall of atria via muscle fibres at regular intervals.