Understand the definition of myocardium, and explore its functions and physical makeup. Then, read about some conditions that can affect this unique type of muscle.

A Silent Condition

Meet Joe. He is 46 years old and has been healthy his entire life, with the exception of a few colds and the normal childhood illnesses. Joe does not smoke, he exercises three times a week, and tries to eat a healthy diet. Joe feels great and is totally unaware that he suffers from a condition that can cause a heart attack at any time. The condition is cardiomyopathy, a disease of the myocardium.

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What Is the Myocardium?

The myocardium is the thick, middle layer of the heart and is composed of cardiac muscle. Cardiac muscle is very unique because it possesses the characteristics of skeletal muscle AND smooth muscle. Skeletal muscle controls the voluntary movement of the body, while smooth muscle is responsible for the movement of all other body organs. The myocardium acts on its own, with no conscious effort.

How Does It Work?

The myocardium is composed of thousands of muscle fibers that are striated (they have multiple striped fibers) and are arranged at irregular intervals throughout the muscle. They connect to each other at points called intercalated discs. These are tiny membranes that separate the ends of the muscle cells. These fibers actually use calcium to cause an electrical conduction to occur.

The contraction (heart beat) of the myocardium is responsible for pumping blood with oxygen to the body. The body requires oxygen for proper function. The heart muscle also pumps deoxygenated blood into the lungs, allowing for replacement of the oxygen so it can be used again. Like all body tissues, the myocardium itself requires a blood supply in order to function; the coronary arteries supply the heart muscle with blood.

Diseases of the Myocardium

The myocardium is obviously integral to having a healthy, working body. When it is unable to function properly, serious conditions can arise — like the ‘silent condition’ mentioned earlier.

Cardiomyopathy is a common disease of the heart in which the myocardium becomes enlarged. While this may seem like a good thing (muscles are meant to get larger, right?), the enlargement actually makes the heart function decrease and interferes with the conduction. The heart can simply stop working.

The bad thing about cardiomyopathy is that it rarely causes symptoms, and people don’t even know anything is wrong until the unthinkable happens. Many young, male athletes have died suddenly because of cardiomyopathy, making it a very noticeable condition.

Another common disease that affects the myocardium is coronary artery disease (CAD). This happens when the arteries that feed blood to the heart muscle become blocked or clogged. When oxygen cannot reach the heart muscle, death of the affected muscle occurs. The end result is a heart attack. Symptoms of CAD include shortness of breath, fatigue, and chest pain.

Lesson Summary

The myocardium is the large, middle part of the heart muscle. It pumps blood to the tissues of the body and is under involuntary control. The myocardium is made up of striated muscle fibers that connect at intercalated discs. Cardiomyopathy and coronary artery disease are two common conditions that affect the myocardium. Cardiomyopathy normally causes no symptoms, while CAD can cause some very noticeable changes.