Preconditioning has been shown to be a powerful technique for reducing infarct size in every animal model tested. There is now evidence that the human heart can be preconditioned by ischemia and pharmacologic agents. Humans can adapt rapidly to brief ischemic insults, as shown by “warm-up” or “ walk-through” angina pectoris. In vitro analysis of human tissue, angioplasty literature, and studies of preinfarction angina have also shown the reality of preconditioning in humans. The mechanisms whereby preinfarction angina confers benefit has been an area of considerable discussion. Preconditioning-like drugs might be administered to produce a cardioprotective effect in patients undergoing open heart procedures, or in patients with unstable angina pectoris or threatened myocardial infarction. Whether these agents could play any role during evolving myocardial infarction is less clear...