The identification of myocardial viability in patients with coronary artery disease and left ventricular dysfunction (LVD) has important clinical and prognostic implications. Two terms commonly used to define clinical conditions of potentially reversible contractile dysfunction are stunned myocardium and hibernating myocardium. Stunned myocardium refers to transient depression of contractile function secondary to an acute ischemic insult. Hibernating myocardium is a form of contractile dysfunction of living myocytes in the setting of chronic ischemia or chronically reduced flow reserve. Numerous observational studies have shown improved clinical outcomes after revascularization of patients with LVD and evidence of myocardial viability, although patients with nonviable myocardium have not been shown to have the same benefits. The use of noninvasive techniques to determine myocardial viability provides important information to guide clinicians in deciding which patients with LVD are likely to receive benefit from a revascularization procedure. Positron emission tomography, single-photon emission computed tomography, dobutamine echocardiography, and cardiac magnetic resonance imaging each have advantages and limitations.