In this, the 1st part of a 2-part review, we discuss how plaque rupture is the most common underlying pathophysiologic cause of unstable angina and non-ST-segment-elevation myocardial infarction and how early risk stratification is vital in the timely diagnosis and treatment of acute coronary syndrome. Part 2 of this review (to be published in a later issue of this journal) will focus mainly on the various pharmacologic agents and treatment approaches (early invasive vs early conservative) to the management of unstable angina and non-ST-segment-elevation myocardial infarction.