Patients 21 years of age and older with hypertrophic cardiomyopathy may be eligible for this study. Candidates will be screened with a medical history and physical examination, electrocardiogram (EKG), blood tests, Holter monitor, and echocardiogram. A Holter monitor is a device about the size of a Walkman that is connected to three wires that are attached to the chest. It is worn for 24 hours to provide continuous monitoring of heart rhythm. An echocardiogram uses a small probe that emits sound waves to produce images of the heart. The probe is moved across the chest and the reflection of the sound waves from the chambers of the heart produce images showing the heart's thickness and function.