the sequence of contraction of the heart chambers is
There are two atrial and two ventricle chambers of the heart; they are paired as the left heart and the right heart -- that is, the left atrium with the left ventricle, the right atrium with the right ventricle -- and they work in concert to traverse the cardiac cycle continuously, (see circular diagram at right margin). 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. During ventricular systole the ventricles are contracting and vigorously pulsing (or ejecting) two separated blood supplies from the heart -- one to the lungs and one to all other body organs and systems -- while the two atria are relaxed (atrial diastole). This coordination ensures that blood is efficiently collected and circulated throughout the body.