unstable angina n angina pectoris characterized by sudden changes (as an increase in the severity or length of anginal attacks or a decrease in the exertion required to precipitate an attack) esp. when symptoms were previously stable
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unstable angina pectoris angina pectoris that occurs unpredictably or suddenly increases in severity or frequency; attacks may occur without provocation, such as during sleep or rest, may not respond to nitroglycerin, and may be of unusually long duration. Prinzmetal angina is often included in this category. Cf. stable a. pectoris.Medical dictionary. 2011.