This information is for people who have unstable angina. It tells you about nitrates, a treatment used for unstable angina. It is based on the best and most up-to-date research.
Do they work?
We don't know. If you take a drug called a nitrate, you should have less chest pain in the first few days after your attack of unstable angina. And the pain may be milder. But there isn't enough research to tell if these medicines can reduce your risk of having a heart attack or of dying.
Still, doctors tend to use nitrates for unstable angina. This is partly because of the way these drugs work on the heart, and partly because doctors know that these medicines help people who have had a heart attack or have stable angina. 
What are they?
Nitrates are drugs that widen blood vessels. This lets more blood flow through them. Doctors call these drugs vasodilators. They work on your arteries and your veins.
If you had a type of chest pain called stable angina before you had your attack of unstable angina, you may already be taking a nitrate drug called glyceryl trinitrate (GTN for short). This same drug is commonly used as a treatment after unstable angina.
If you are in a lot of pain, as is likely with unstable angina, the quickest and best way to get nitrates is through a drip in a vein (also called an intravenous infusion, or IV for short). You will probably have this drip for at least 24 hours.
The two nitrate drugs used for this are glyceryl trinitrate (GTN) and isosorbide dinitrate.
How can they help?
Being on a drip of a nitrate for 48 hours to treat unstable angina will reduce your risk of:
Having short attacks of chest pain (stable angina)  
Having a new longer attack of chest pain (unstable angina)  
Having to take nitrate tablets for your chest pain. 
How do they work?
Nitrates widen your blood vessels by relaxing the muscles in their walls. They relieve chest pain because they widen the coronary artery that is blocked. And this lets more blood pass through it. More blood means more oxygen for your heart, and that means less pain.
Nitrates don't have any effect on the clot that's causing your unstable angina. But they do stop your coronary arteries tightening around the blockage and making it worse.
Can they be harmful?
Like all drugs, nitrates have side effects. But they are usually mild. Doctors think that nitrates are pretty harmless because researchers have not found any serious side effects during studies.
These are some of the side effects they can cause.
Headaches: Nitrates widen the blood vessels in your brain. This can cause a throbbing headache that starts soon after treatment.
Dizziness and fainting: If you get up too quickly after being on a nitrate drip, you may feel dizzy or even faint. Normally, your leg veins tighten as you stand up to stop blood pooling in your legs. Nitrates can stop this happening. So your blood pressure drops and you feel faint.
Reddening or flushing of your skin: Nitrates widen the small blood vessels in your skin. This can make it turn red and feel warm, like when you blush.
Most nitrates act for a short time. That means the side effects wear off quickly. But if you have side effects while you're on a nitrate drip, they may last until the drip is stopped.