During ventricular diastole:
(a) The auricles relax
(b) The heart contracts
(c) The heart pumps
(d) None of them

Hint: The phase of the heartbeat when there is a relaxation in the heart muscles, which allows the chambers to fill with blood. Only 25% of the ventricle filling is possible during the ventricular diastole.

Complete answer:
During this phase of the cardiac cycle, only the ventricles are in the relaxed state while the auricles remain in the contracted state. As a result, the filling of the ventricles takes place due to the opening of two atrioventricular (AV) valves.
- Atrial systole: It involves the contraction of atria from the anterior to the posterior side which pushes blood to the respective ventricle. It increases the blood flow of the ventricle by 30 percent. It is also called as mid- late diastole. There is no reflux of blood from the auricles to the large veins.
- Ventricular systole: It involves the simultaneous relaxation of the atria and contraction of the ventricles. The ventricular systole takes about 0.3 seconds while the ventricular diastole takes about 0.5 seconds.
- Joint diastole: All the chambers during this phase are in a relaxed phase. During complete diastole, blood from the great vein flows into the atria.
- The sequence of events that occur during one heartbeat is called a cardiac cycle.

So, the correct answer is, ’None of them.’

Note: The heart has four chambers, the upper two chambers are called the auricles and the lower two chambers are called the ventricles. All the chambers do not beat simultaneously. Right and left auricles to contract simultaneously while right and left ventricles contract after the contraction of auricles has ended. The auricles relax while the ventricles contract.