Which statement best describes the primary effect of nitrates in reducing myocardial oxygen demand?

• A. Venodilation reducing preload
• B. Increase afterload
• C. Increase heart rate
• D. Inhibit coronary arteries

Answer: (A)

Nitrates primarily reduce myocardial oxygen demand by dilating veins, which lowers venous return to the heart. This venodilation decreases preload, reducing left ventricular end-diastolic volume and filling pressures. With less stretch and work required by the heart during each beat, myocardial oxygen consumption falls. At typical therapeutic doses, this preload reduction is the dominant effect, though higher doses can also dilate arteries and modestly lower afterload, providing an additional decrease in oxygen demand. Increasing afterload or heart rate would raise oxygen demand, and nitrates do not work by inhibiting coronary arteries; their benefit comes from reducing the heart’s workload through venous dilation and, to a lesser extent, arterial effects.