What is the primary therapeutic effect of diltiazem-SR?

• A. Vasodilation due to calcium channel blockade
• B. Increased cardiac contractility
• C. Decreased heart rate via beta-blockade
• D. Increased aldosterone secretion

Answer: (A)

The main idea is that diltiazem-SR works by blocking calcium entry into vascular smooth muscle, causing relaxation and dilation of arterial vessels. This vasodilation lowers systemic vascular resistance and blood pressure, which is the primary therapeutic effect in conditions like hypertension and angina. The drug does have other effects—such as slowing heart rate by acting on the SA/AV nodes and possibly reducing contractility—but these are secondary to the main vasodilatory action. Increased cardiac contractility would not be expected with this medication, beta-blockade is not how it works, and increasing aldosterone secretion is not related to its mechanism.