Morphine is used to relieve pain and anxiety. What other functions does morphine perform in a patient with ACS?

• A. Increases systemic vascular resistance
• B. Decreases preload and may decrease afterload
• C. Dilates pulmonary arteries to raise oxygenation
• D. Increases heart rate

Answer: (B)

Morphine in ACS helps reduce the heart’s workload by lowering both the venous return and, to some extent, the arterial resistance. The primary effect is venodilation, which decreases preload—the amount of blood filling the heart before it contracts. When preload drops, the heart stretches less, so the oxygen demand to pump that blood down the circulation falls. There can also be some arterial dilation, which lowers systemic vascular resistance and may decrease afterload, further reducing myocardial oxygen consumption. This combination helps relieve ischemia beyond pain and anxiety relief.

It does not raise systemic vascular resistance, so the idea that morphine increases afterload isn’t accurate. It doesn’t primarily dilate pulmonary arteries to improve oxygenation, which isn’t a primary or reliable effect of morphine. It also doesn’t typically increase heart rate; it usually reduces sympathetic drive, which can blunt or slow the heart rate rather than raise it.