Calcium channel blockers are a class of drugs used in treating cardiovascular diseases such as angina, arrhythmias (irregular
rhythms), and hypertension. Calcium is required for the contraction of heart muscle cells, and by altering the movement of calcium across channels in heart cell walls, calcium channel blockers help to suppress irregularities in heart rhythms. Calcium is also important for the blood vessels, where it helps control blood
pressure. Calcium channel blockers relax arterial smooth muscle, and are therefore used to treat hypertension. Verapamil, nifedipine, and diltiazem are types of calcium channel blockers with similar but not identical sites of action.
Because heart muscle relies on calcium entry into cells to
function properly, calcium channel blockers may limit the heart's ability to function normally. Dangerous side effects include suppression of cardiac function, leading to congestive heart failure, slow heart rates, and low blood pressure. Newer calcium channel blockers, including amlopdipine and felodipine, have less of an inhibitory effect on cardiac muscle contractility and function.