Scintigraphic detection of myocardial viability is required for treatment planning and prognostication in patients with contractile dysfunction. There are four pathophysiological entities of dysfunction in coronary artery disease; one of them, "hibernating" myocardium, cannot be differentiated from scar or necrosis by mere perfusion imaging. Due to the determinants of delayed activity distribution after 201Tl injection, optimized imaging protocols using this tracer allow for adequate differentiation in many instants. Differentiation between "stunned" and "hibernating" myocardium or scar is achieved with all perfusion indicators actually available. Though 201Tl imaging with optimized protocols is almost as efficacious in viability detection as 18F-FDG positron emission tomography, the latter actually remains the reference method particularly in patients with severe left ventricular dysfunction at coronary occlusions.