Studies of the mechanism of action of a variety of cardiovascular drugs will be carried out in man. Drugs under study are propranolol, digoxin, theophylline, quinidine, and procainamide. Also, the endocrine response to angiotensin inhibitors will be studied (NE, renin, and aldosterone). Primary attention will be directed to correlating function responses of the cardiovascular system to specific blood levels of these drugs.