Indications for Atenolol + Chlorthalidone Beta blocker and thiazide diuretics are given in combination to treat hypertension. Atenolol reduces the work load on the heart and Chlorthalidone reduce the hypertension by increasing the flow of urine. 1. Hypertension Mechanism of Action of Atenolol Atenolol is a cardio selective beta-1 adrenergic antagonist. It has negative chronotropic and negative inotropic effects on heart. It decreases oxygen consumption- cardiac work and aortic pressure. It decreases nor adrenaline and renin releases. It decreases central sympathetic out flow In sympathetic over activity, it prolongs systole by retarding conduction. It increases oxygen supply and exercise tolerance in angina patients. The drug decreases BP in hypertensive individuals- both systolic and diastolic BP is reduced. Antimigraine action: Atenolol is useful in migraine due to its beta blockade action. Through beta blockade action it inhibits vasodilation and relieves migraine.