Angina is chest pain or discomfort that occurs when your heart doesn't get as much blood and oxygen as it needs. Over time, the coronary arteries that supply blood to your heart can become clogged with plaque. If one or more arteries are partly clogged, not enough blood can flow through, and you can feel chest pain or discomfort. Reversible (stable) angina occurs when the heart works harder and needs more oxygen, and goes away when heart demand is decreased. Progressive (unstable) angina occurs when a plaque in one or more of your coronary arteries ruptures (bursts). If the buildup happens rapidly, you are at risk for a heart attack.