THE HEART MUSCLE

The heart is a muscular pump that propels blood by squeezing it of the powerful ventricles into the arteries. The muscular wall of the heart has three layers: a thin inner lining (endocardium), the bulk of working muscle (myocardium), and the outer surface (epicardium). The squeezing action of the heart is produced by coordinated shortening of the muscle fibers that make up the walls of the heart. When the muscles shorten (contract), the ventricular chambers become smaller forcing blood out. The valves ensure that the blood goes out the right direction. This phase of the heart action is systole. After contracting the heart muscle relaxes, the muscle fibers lengthen, the ventric chambers become more spacious, and blood flows into them from the atria. This phase is diastole.

Normal

The nuclear "MUGA" scans (at right) show a normal heart. The orange ventricles (arrow points to left ventricle) are large during diastole and contracted during systole.

Dilated

The nuclear "MUGA" scans (at right) show a weakened heart. It cannot squeeze as hard. The size of the ventricles changes very little between diastole and systole.

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Cardio & Blood-holesterol