Hibernating myocardium (HM) is a result of reduced myocardial blood flow that causes impaired left ventricular (LV) function at rest and can be reversed by revascularization. Although HM is not ischemia “in the strict sense,” it may be viewed as an example of an “exquisitely regulated tissue successfully adapting its activity to prevailing circumstances.” The clinical diagnosis of HM is based on documenting an area of LV dysfunction at rest with viable myocardium. HM has been demonstrated to occur in chronic and unstable angina, acute myocardial infarction, heart failure and/or severe LV dysfunction, and anomalous origin of the left coronary artery from the pulmonary artery. HM is characterized as clinically acute, subacute, or chronic on the basis of the rate of recovery of resting LV dysfunction after revascularization and the study of the morphologic changes in the dysfunctioning myocardium. However, such a classification into three precisely separated states may be somewhat arbitrary and HM may be best described as a spectrum. The outcome of patients with coronary artery disease is determined not only by the extent and severity of the disease, but also by the amount of HM and LV myocardium that is or can be irreversibly damaged. Successful revascularization of the HM is able to reduce LV dysfunction and the amount of myocardium at risk...