A client is taking a calcium channel blocker (CCB). The nurse knows to monitor for which of the following dangerous side effects of this medication?

A. Calcium channel blockers can cause or exacerbate heart failure due to their effects on myocardial contractility and fluid balance. Monitoring for signs of worsening heart failure is crucial. B. While drowsiness can occur, it is not typically considered a dangerous side effect of calcium channel blockers. C. Headache is a common side effect of CCBs, but not usually dangerous compared to heart failure. D. Calcium channel blockers are used to treat hypertension, so they typically would not cause dangerous hypertension.