Why unstable angina is a contra indicator for stress test?

Heart attack: With unstable angina the cardiologists do not like to do a stress test because the stress on the heart could precipitate a heart attack. If they need to examine the heart in someone with unstable angina they are more likely to do a coronary angiogram so they can look directly at the vessels without stressing the heart. Also with the do the angiogram they may be able to place a stent for treatment.