Answer:
Myocardium.
Step-by-step explanation:
Heart is the main pumping organ of the body. Human heart is divided into four chambers two atria and two ventricles. The human heart consists of three layers- epicardium, myocardium, and endocardium.
The middle layer of the heart (myocardium) consists of cardiomyocytes or the muscle cells. These cells receive nerve stimulation from the atrioventricular nodes and sinoatrial nodes.
Thus, the answer is myocardium.