What is the mechanism of action of nitrates in ischemia?

• A. Venodilation reducing preload
• B. Increase heart rate
• C. Increase afterload
• D. Block beta receptors

Answer: (A)

Nitrates relieve ischemia mainly by decreasing myocardial oxygen demand through venodilation that reduces preload. They release nitric oxide, causing smooth muscle relaxation in veins, which lowers venous return to the heart. With less preload, left ventricular end-diastolic volume and wall stress fall, so the heart works less hard and requires less oxygen. This shift in the oxygen supply-demand balance helps alleviate ischemia and angina.

At higher doses, nitrates can also dilate arteries and reduce afterload, but the primary effect is preload reduction. The other options don’t fit because increasing heart rate would raise oxygen demand, increasing afterload would worsen ischemia, and blocking beta receptors is the action of beta-blockers, not nitrates.