5. Concomitant therapy: Patients will be allowed to be on comcomitant therapy with aspirin, statins, thiazide diuretics, calcium antagonists (for treatment of hypertension), clonidine, vasodilators, or angiotensin antagonists. Patients will be on stable medical therapy for at least 2 months before recruitment. Patients with previous treatment with beta adrenergic blockers (metoprolol, propranolol, atenolol, and labetalol) will also be eligible to participate, but will be randomized to the study beta blocker.