The myocardium is the thick middle layer of cardiac tissue, sandwiched between the epicardium and endocardium.
In Our Own Words
The myocardium is the heart’s thick muscular middle layer, located between the outer layer (i.e., epicardium) and the inner layer (i.e., endocardium). The myocardium is made up of highly specialized heart muscle cells that are continually contracting, day and night, and depend on a steady and rich flow of blood for oxygen and nourishment.
A heart attack occurs when the coronary artery that feeds a section of the heart muscle becomes blocked and causes cells in that area to die. This small area of dead tissue is also called an infarct; hence, the name myocardial infarction for a heart attack.