Question

The rhythmic contraction and expansion of heart is ________.

Answer 1

Hint: The contraction of heart is called cardiac systole, whereas expansion or relaxation is called cardiac diastole. We can altogether call it a cardiac cycle.

Complete answer:
The rhythmic contraction and expansion of the heart is a Cardiac cycle.
In order to answer the question, we first should be able to understand what cardiac cycle is.
So, in simple terms, the cardiac cycle is one heartbeat, from start to end. This one full cycle of heartbeat contains a series of events of pressure changes that occur in the heart. These movements help in blood pumping. Blood is pumped out of the heart during contractions, whilst the heart is filled with blood during relaxation.
The cardiac cycle involves four major stages, of single heartbeat activity:
1) Isovolumic relaxation
2) Inflow
3) Isovolumic contraction
4) Ejection
Cardiac diastole is the time of the cardiac cycle where, right after contraction the heart relaxes and expands, whilst refilling with blood returns from the circulatory system.
Atrial systole is the contraction of cardiac muscle cells, of both atria followed by electrical stimulation and conduction of electrical currents through the atrial chambers.
Ventricular systole is the contraction, followed by electrical stimulations of ventricular syncytium of cardiac muscle cells in the right as well as left ventricles.

Note:
Action of cardiac cycle is involuntary.
In normal human beings, the duration of one cardiac cycle is about 0.6-1 sec.
Electrical stimulations/impulses are produced by pacemaker cells, found in sinoatrial and atrioventricular nodes.