Despite thousands of publications describing agents that limit infarct size in animals, all we have available today is reperfusion therapy. In this review, we examine why these drugs have not been translated into clinical practice. Many of the first interventions tested in clinical trials were very controversial in animal trials and their actual efficacy is still in question. Interventions based on the preconditioning mechanism have been very reproducible in animals, but clinical testing of them has just begun. Only approximately 25% of reperfused patients have infarcts large enough to put them at risk of heart failure and would require additional treatment. Inclusion of the 75% of patients with small infarcts in treatment groups has greatly diluted the significance of data in past clinical trials. Size of the risk zone has emerged as a reliable way to identify the vulnerable 25%. Recent small-scale clinical trials using risk stratification algorithms have shown clear infarct size limitation using ischemic and pharmacological postconditioning, confirming that the human heart responds like hearts of animal models. Most cardioprotectants have been studied in healthy animals, but recent studies indicate that aging and diabetes, common in coronary patients, do interfere with preconditioning-based interventions in animals. Clearly more study is needed to identify which interventions are adversely affected by comorbidities. (Circ J 2009; 73: 1171-1177)