Angina
"I have had heart disease for many years and always have a bottle (tiny!) of sub-lingual nitros in my pocket. When I feel chest pain, one under the tongue and the pain goes away, in my case, every time. The nitro works very quickly to dilate your blood vessels allowing more blood and oxygen to get to your heart muscle. Ask your doctor how to proceed should one pill not relieve the pain.

Sub-linguals have a limited life once the bottle is opened the first time, about 3-6 months. If you find yourself using all the pills within that time (25 tiny tablets, typically), then they are best. If you only need it occasionally, get the pump spray as it has a much longer life. It is, however, more expensive."