Cardiac output is the volume of blood pumped by one ventricle of the heart in one minute.

cardiac output = heart rate × stroke volume

Diastole is the phase of the cardiac cycle where the heart relaxes.

Blood flows into the atria through the pulmonary vein and the vena cava, pushing open the atrioventricular valves and filling the ventricles.

During atrial systole, the atrial walls contract, forcing the remaining blood into the ventricles.

Throughout this stage, the muscle of the ventricle walls remains relaxed.

During ventricular systole, the ventricle walls contract simultaneously, increasing blood pressure within them.

This closes the atrioventricular valves and forces blood into the aorta and pulmonary artery.

The basic rhythm of the heart is maintained by a wave of electrical excitation, which travels through the following structures in this order:

1. Sinoatrial node (SAN) - initiates the heartbeat by stimulating the atria to contract
2. Atrioventricular node (AVN) - picks up the electrical activity from the SAN and imposes a slight delay
3. Bundle of His - receives electrical activity from the AVN to the apex of the heart
4. Purkyne fibres - conduct the wave of excitation from the apex of the heart upwards, stimulating the ventricles to contract

The delay at the AVN ensures that the atria have finished contracting and emptying their blood into the ventricles before the ventricles start to contract. This maximises the efficiency of the heart's pumping action.

Valves in the heart ensure blood flows in one direction.

Valves open when pressure differences favour movement in the required direction and close when pressure differences would cause blood to flow in the opposite direction.

The heart is referred to as myogenic because it can contract and beat without receiving signals from nerves. This is due to special cells in the heart that can generate and spread electrical impulses.