Losastrum BETA Tablet is a combination of two blood-pressure lowering medicines: Atenolol and Losartan. Atenolol is a beta blocker which works specifically on the heart to reduce heart rate and lower blood pressure. Losastrum is an angiotensin receptor blocker (ARB). Losastrum works by blocking the hormone angiotensin thereby relaxing blood vessels. Together they allow the blood to flow more smoothly and the heart to pump more efficiently.