Question

The bulk of the heart wall is the thick, contractile middle layer called the

Answer 1

The thick, contractile middle layer of the heart wall is the myocardium, composed of cardiac muscle cells.

Step-by-step explanation:

The thick, contractile middle layer of the heart wall is called the myocardium. It is the bulk of the heart wall and consists mainly of cardiac muscle cells. The myocardium is responsible for pumping blood through the heart and into the major arteries.