• The illustration on the upper right shows a cut through the wall of the heart. The "meat" is the myocardium, the muscular layer of the heart. You can see through that cut on the painting of the heart with the piece missing, and see that the heart is hollow, blood would normally be flowing inside its hollow chambers.
• Myocardium not only makes up the bulk of the wall of the heart, but also moves - it is the myocardium that works to pump the blood. So, healthy myocardium is vital for both structural and functional reasons.

A heart attack is called a myocardial infarction because those two words literally describe what has happened to the heart during the attack. "Infarct" is any area of dead and damaged tissue caused by a sudden and complete loss of blood supply. A heart attack occurs if a portion of the myocardium suffers an infarct. It happens after one or more of the coronary arteries is completely blocked. Depending on the amount of myocardium damaged, it's sometimes called "slight" (for a small amount), moderate, or "massive" (if a very large portion of the myocardium has been damaged.)

Knowing something about the nature of this muscle tissue allows a better understanding the heart, heart attacks, and other conditions that affect it, like myocarditis.

• Myocardium is a special kind of muscle tissue. Each cardiac muscle cell has properties that are qualitatively different than muscle cells in the arms and legs, which are called skeletal muscles (like the biceps and triceps). Cardiac muscle is also different from the smooth muscle that coats a layer of the GI tract , the bladder, uterus and many other structures. Only the heart has this tissue.
• That makes intuitive sense to those who know the body, because the behavior of the heart muscle is so unique.
  • The cardiac muscle beats endlessly throughout life, and contracts in a co-ordinated way because the impulse to do spreads from cell to cell.
  • Those attributes enable this tissue to be the life pump of the circulatory system, a pump that keeps pumping steadily and that can push the blood in a given direction - with the use of one-way valves, anyway.

The ways that the muscle is damaged by loss of its blood supply in a myocardial infarction reflect this tissue's unique nature, and come into play in the treatment of heart attacks, and in the signs of symptoms of ischemia. [Ischemia is a drop in the blood supply - not to the point of killing (that would be an infarct), but to the point where the tissue's function is limited by limitations in the blood supply.]

Understanding a bit about the myocardial tissue also helps in understanding what happens when that tissue becomes inflamed, in myocarditis ("inflammation of the myocardium").

• Myocardium (and Myocarditis)