What are the top reasons for getting unstable angina?

Heart disease.: Unstable angina is usually due to a plaque rupture which limits the blood flow to an area of the heart. This is caused by increase in the size of the plaque or, elevated blood pressure or increased heart rate which make the narrowing more likely to occlude the artery. This causes a change in the usual angina, or the onset of new angina or cardiac chest pain.

Plaque rapture: Rapture of an atherosclerotlic plaque is the most common cause of unstable angina often associated with active inflammation within the plaque.