Atenolol and chlorthalidone combination is used to treat high blood pressure (hypertension). High blood pressure adds to the workload of the heart and arteries. Atenolol + Chlorthalidone is a combination of two blood-pressure lowering medicines:  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. Chlorthalidone 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.