nitrate

Nitrates relieve the chest pain of angina by widening blood vessels. Once in the body they release nitric oxide, the same molecule the lining of healthy vessels uses to signal relaxation, so the smooth muscle in the vessel walls loosens and the vessels open up.

The biggest relief comes from dilating the veins, which lets blood pool in them and reduces the volume returning to the heart. With less to pump, the heart's oxygen demand falls, and angina eases; nitrates also help by opening the coronary arteries themselves, especially in spasm.

A tablet or spray of nitroglycerin under the tongue works within minutes for an angina attack, while longer-acting forms are taken to prevent attacks. To keep them working, a daily nitrate-free interval is usually built in, because the body otherwise develops tolerance.

Common effects are headache, flushing, and a drop in blood pressure that can cause light-headedness. A critical caveat: nitrates must never be combined with erectile-dysfunction drugs of the PDE5-inhibitor type, as the pair can cause a dangerous, sometimes fatal fall in blood pressure.