calcium channel blocker

Muscle cells in the heart and blood vessels need calcium to flood in before they can contract. Calcium channel blockers partly close the gates that let that calcium in, so vessel walls relax and the heart squeezes a little less forcefully — like easing the grip on a clenched hose.

There are two practical families. The dihydropyridines, with names ending in “-dipine,” act mainly on blood vessels, opening them to lower blood pressure and relieve angina. The non-dihydropyridines, verapamil and diltiazem, act more on the heart's electrical system, slowing the rate and helping control certain fast rhythms.

Because of this split, they are chosen for the job at hand: a vessel-acting one for hypertension, or a heart-acting one to slow the ventricular rate in atrial fibrillation. They are especially valued for a particular form of angina caused by coronary artery spasm.

The caveats follow from their targets. Vessel-acting agents can cause ankle swelling, flushing, and headache, while the heart-acting ones can slow the heart too much and should generally not be combined with beta-blockers or used in a weak, failing pump.