Hibernating myocardium occurs when significantly reduced blood flow affects a segment of the myocardium, causing dysfunction on a chronic basis. If blood flow is restored via percutaneous coronary intervention (PCI) or surgical bypass grafting, the function can return to normal. Viability testing can help determine if myocardium is hibernating or completely infarcted. Viability testing is best performed using magnetic resonance imaging (MRI), but can also be achieved with PET scanning (positron emission tomography), thallium myocardial perfusion imaging and dobutamine stress echocardiography.