The principal mission of the NIH is the conduct of research that elucidates biological mechanisms, pathogenesis, and treatment of disease. Patients with known or suspected cardiovascular diseases are referred to NHLBI cardiologists for consideration of participation in clinical research protocols. However, eligibility for participation is often uncertain from referral information or even after an outpatient evaluation. The purpose of this protocol is to permit inpatient evaluation of patients for whom participation in clinical research protocols is under consideration in order to determine protocol eligibility by means of conventional laboratory and cardiovascular testing.