Exercise testing performed earlier than six weeks post-MI is accepted as "standard" medical practice. Although both heart rate-limited and symptom-limited exercise protocols are used with nearly equal frequency, the latter appears more valuable because the prognostic yield is greater without sacrificing patient safety. Treadmill or cycle ergometers are the preferred modes of testing because of higher exercise work loads imposed and increased sensitivity and specificity of results. The physiologic exercise responses to graded work loads among these acute MI survivors include a mean maximal heart rate range of 118 to 136 beats/min, a peak systolic blood pressure between 137 and 170 mmHg, a mean peak double product from 16,000 to 22,400, and a mean maximal work load between 4.8 and 7.0 METS. Exercise findings which are most clinically useful are greater than 1 mm ST segment depression from rest level, presence of angina pectoris during exercise, decrease in systolic blood pressure with increasing work, presence of complex or frequent VEBs, and exercise tolerance less than 4 METS. These exercise findings identify, in recent post-MI survivors, groups of patients that have significantly different estimated future cardiac morbidity and mortality rates. The most consistent indices of multi-vessel coronary heart disease are ST segment depression, angina pectoris, and poor exercise tolerance. The most important role of stress testing in this period post-MI is identification of individuals who urgently need evaluation for coronary bypass surgery. In addition to risk stratification, exercise testing provides valuable information regarding exercise prescription for cardiac rehabilitation, direct psychologic benefit for resuming an active lifestyle, and motivation for exercise participation. Although safety of the early post-MI stress test has not been systematically studied, reports from individual studies indicated low morbidity and mortality. Attesting to this is the frequency with which it is performed as a routine office procedure. Finally, there has been a growing use of this procedure not only among cardiologists but also among internists and family practice physicians.