A doctor tells her nursing students that it is important to monitor patients' blood pressure when they are receiving verapamil (a calcium channel blocker). Why?

Calcium channel blockers inhibit the movement of calcium ions from the interstitial fluid into cardiac and smooth muscle cells. This would cause a decrease in heart rate, stroke volume, and cardiac output. These in turn would lower blood pressure. In addition, the calcium channel blockers would also inhibit contraction of the smooth muscle in the wall of blood vessels, causing them to get wider and thus also lower blood pressure. Because both heart and smooth muscle cells are inhibited by verapamil, its effects on blood pressure are particularly potent.