The identification of viable myocardium in patients with coronary artery disease and left ventricular dysfunction is an issue of increasing clincal relavance in the current era of myocardial revascularization. There are at least two forms of reversible myocardial dysfunction. Early reperfusion does not always lead to immediate functional improvement; rather, the return of contractility in tissue salvaged by reperfusion is delayed for hours, days or even weeks, a phenomenon that has been termed "stunned myocardium". Some patients with coronary artery disease show myocardial dysfunction ar rest which are associated with reduced perfusion, and which disappear after revascularization; this phenomenon has been termed "hibernating myocardium". Recently, cardiac imaging techniques that evaluate myocardial viability on the basis of perfusion contraction mismatch and inotropic reserve have gained substantial popularity and clinical success. This review focus on the application of 201T1 and Tc-99m-MIBI to address myocardial viability in patients with hibernating and stunned myocardium. It is clear that 4-hour redistribution images of 201T1 underestimate ischemia and overestimate scar. Delayed imaging and reinjection imaging have been developed for the assessment of viability. Among many protocols suggested, stress-redistribution-reinjection imaging gained most popularity. Although Tc-99m- MIBI could identify myocardial viability, 201T1 reinjection technique was regarded as superior to it. In conclusion, 201T1 stress, 4-hr rest redistribution, and reinjection imaging technique may be the most preferable method for evaluation of myocardialviability.