Hypertrophic cardiomyopathy is described as either obstructive or nonobstructive.

• In nonobstructive hypertrophic cardiomyopathy, the heart muscle is abnormally thick but not to the extent that any part of it crowds the lower heart chambers (ventricles). The thicker muscle simply cannot relax properly. This means less blood can enter the chambers and less blood is circulated to the body. In addition, abnormal heart rhythms may develop. Most people with hypertrophic cardiomyopathy have this type.
• In obstructive hypertrophic cardiomyopathy, portions of the heart muscle become so thick that they bulge out into the lower heart chambers (ventricles). Blocked blood flow and smaller, less effective ventricles result, especially during exercise, when the heart has less time to relax and fill. Thickened heart muscle may also interfere with how the heart valves open and close, particularly the mitral valve, which divides the left upper chamber (atrium) from the left ventricle.