Which of the following is an effect of nitroglycerin spray?

• A. Constricts arteries.
• B. Increases heart rate.
• C. Dilates veins to reduce preload.
• D. Relaxes veins to reduce preload.

Answer: (C)

Nitroglycerin spray works by releasing nitric oxide, which relaxes vascular smooth muscle. At typical therapeutic doses, it mainly causes venodilation—the veins widen more than the arteries. When veins dilate, more blood pools in the peripheral circulation and less returns to the heart, so the preload (the volume of blood in the ventricles at the start of systole) decreases. With lower preload, the heart doesn’t have to stretch as much, reducing myocardial wall tension and oxygen demand. This helps relieve angina symptoms quickly. While nitroglycerin can also cause arterial dilation and lower blood pressure at higher doses, the primary, most characteristic effect described here is venous dilation leading to reduced preload.