There are three basic types of cardiomyopathy:
1. dilated cardiomyopathy. The heart muscle becomes weak and the heart chambers subsequently enlarge (dilate).
2. hypertrophic cardiomyopathy. The heart muscle itself is much thicker than normal.
Dilated cardiomyopathy refers to overall enlargement (dilatation) of the heart chambers, especially the ventricles. Although this enlargement is a key part of dilated cardiomyopathy, it is not the initial problem, but rather the heart's own response to a weakness of heart muscle and poor pumping ability. The weakness of the heart muscle in this condition is generalized, "global" - all parts of the myocardium are affected about equally. Enlargement of the heart is the heart's way of trying to compensate for the weakness of its muscle. This is called a compensatory mechanism.
If the heart muscle is weak, it is unable to pump out the same portion of blood that it could at normal strength. Rather than simply "accepting" the limitations of decreased pumping ability, the heart and other organs of the body undergo compensatory changes to try to maximize their efforts.
Dilated cardiomyopathy causes heart failure - an inability of the heart to provide an adequate supply of blood to the body's organs and tissues - which if left untreated is always associated with excess fluid retention, congestion in the lungs and liver, and swelling of the legs.
Hypertrophic cardiomyopathy is an overgrowth of heart muscle that can impair blood flow both into and out of the heart. The disease is characterized by a disorderly growth of heart muscle fibers, causing the heart chambers to become thick-walled and bulky. All the chambers are affected, but the thickening is generally most striking in the walls of the left ventricle. Most commonly, one of the walls, the septum, which separates the right and left ventricles, is asymmetrically enlarged. The distorted left ventricle contracts, but the supply of blood to the brain and other vital organs may be inadequate because blood is trapped within the heart during contractions.
Hypertrophic cardiomyopathy is sometimes called idiopathic hypertrophic subaortic (beneath the aorta) stenosis, abbreviated IHSS. This overgrowth creates a bulge that protrudes into the ventricular chamber and impedes the flow of blood from the heart to the aorta and the rest of the body.
When this obstruction is present, the cardiomyopathy is also called hypertrophic obstructive cardiomyopathy (HOCUM, often pronounced "hokum"). In this condition, the problem is not that the heart muscle is weak but that the overgrown heart muscle impedes the flow of blood through and out of the heart.
Restrictive cardiomyopathy is less common than the other two forms. It can stem from infiltration of the heart muscle with abnormal material (for example in amyloidosis) or with any other type of chronic fibrosing process. The result is a heart that cannot expand sufficiently to fill with blood, and cannot contract efficiently such that adequate amounts of blood perfuse either the lungs for oxygenation, or the tissues for normal blood supply.