In this article, the role of nuclear medicine modalities in assessing myocardial viability and risk stratification in patients with advanced left ventricular (LV) dysfunction are reviewed. Diagnosis of reversible LV dysfunction in patients with heart failure is an important clinical issue. Patients with severe LV dysfunction who have viable myocardium are the patients at highest risk because of the potential for ischemia but at the same time benefit most form revascularization. It is important to identify viable myocardium in these patients, and nuclear medicine techniques are an excellent tool for this. Single-photon emission computed tomography (SPECT) in combination with myocardial perfusion tracers plays an important role in the identification of tissue viability in myocardial segments. Imaging with positron emission tomography (PET) tracers allow the assessment of physiologic processes such as myocardial oxygen consumption, metabolic rate of glucose utilization, and myocardial blood flow. Metabolic imaging with PET offers regional tissue viability in patients with advanced coronary artery disease and severely impaired LV function.