The heart
Thick muscular rhythmically contracting organ consists of 4 chambers (2 atria & 2 ventricles).
The heart is a modified blood vessel that serves as a double pump and consists of four chambers.
On the right side, the atrium receives blood from the body and the ventricle propels it to the lungs. The left atrium receives blood from the lungs and passes it to the left ventricle, from which it is distributed throughout the body. The wall of the heart consists of three basic tunics or layers an inner lining layer, a middle muscular layer, and an external layer of connective tissue.
The wall of the heart consisted of inner lining layer (endocardium), middle muscular Layer (myocardium) and outer layer (epicardium)