Question

what is the rhythmic contraction/ expansion of the heart muscles called​

Answer 1

Answer:

Cardiac cycle is the rhythmic expansion and contraction of heart.

Contraction is called cardiac systole

Relaxation is called cardiac diastole

Together they known as cardiac cycle.

The rhythmic sequence of contractions of the heart is coordinated by two small groups of cardiac muscle cells called the sinoatrial (SA) and atrioventricular (AV) nodes.

Explanation:

Answer 2

Answer:

The rhythmic sequence of contractions of the heart is coordinated by two small groups of cardiac muscle cells called the sinoatrial (SA) and atrioventricular (AV) nodes.