DefinitionUnstable angina is a condition in which your heart doesn't get enough blood flow and oxygen. It may be a prelude to a heart attack.Angina is a type of chest discomfort caused by poor blood flow through the blood vessels (coronary vessels) of the heart muscle (myocardium).See also:Stable anginaVariant anginaAlternative NamesAccelerating angina; New-onset angina; Angina - unstable; Progressive anginaCauses, incidence, and risk factorsCoronary artery disease due to atherosclerosis is by far the most common cause of unstable angina. Atherosclerosis is the buildup of fatty material called plaque along the walls of the arteries. This causes arteries to become less flexible and narrow, which interrupts blood flow to the heart, causing chest pain.At first, angina may be considered stable