Which type of medication lowers heart rate at rest and during exertion?

• A. Loop diuretics
• B. Beta receptor antagonists
• C. Alpha-1 receptor antagonists
• D. Angiotensin-converting enzyme inhibitors

Answer: (B)

Blocking sympathetic signals to the heart slows its pace. Beta receptor antagonists, or beta-blockers, bind to beta-1 receptors in the heart and blunt the usual adrenaline-driven increase in heart rate. This reduces the rate of spontaneous firing of the SA node and slows conduction through the AV node, so heart rate drops both at rest and during exertion. They also lower myocardial oxygen demand by reducing contractility, which helps during exercise. Other options don’t primarily slow the heart rate: loop diuretics decrease blood volume without directly affecting heart rate; alpha-1 antagonists mainly cause vasodilation; ACE inhibitors lower blood pressure and afterload but don’t directly reduce heart rate.