Atenolol + Hydrochlorothiazide is a combination of two blood-pressure lowering medicines: Atenolol and Hydrochlorothiazide. Atenolol is a beta blocker which works specifically on the heart to reduce heart rate and make the heart more efficient at pumping blood throughout the body. Hydrochlorothiazide is a diuretic which lowers blood pressure by removing extra water and certain electrolytes from the body. Over time it also relaxes blood vessels and improves blood flow.