PET of the myocardium in patients with low ejection fraction has classically focused on identifying ischemic and viable myocardium. In this review, we use a case-based format to challenge these simplistic notions while integrating the results from recent clinical trials. The basic message is that, for most patients, severely reduced left ventricular function is due predominantly to nonischemic cardiomyopathy, not scar or ischemia. Consequently, we emphasize several practical pitfalls when using cardiac PET imaging in this population to improve its clinical value.