Which layer of the heart undergoes involuntary contraction and relaxation and makes the heart beat and pump blood into the system? a. endocardium b. myocardium c. epicardium d. pericardium

The correct answer is B. Myocardium

Explanation:

Our heart is made up of three layers which are epicardium, myocardium, and endocardium. The outer layer is epicardium, the middle layer is myocardium and the innermost layer is endocardium.

The majority of the mass and thickness of the heart is myocardium. Myocardium is muscular layer that is made from cardiac muscle tissue and is responsible for contraction and relaxation which results in pumping of blood and heartbeat. Therefore the correct answer is B.

which ever one is showing doing the same exercise in time intervals such as 30 seconds or a minute several times.