Myocardial dyssynergy does not necessarily indicate myocardial necrosis in patients with coronary artery disease. The differentiation between viable and non-viable tissue is of great clinical importance in order to make the most appropriate clinical decision in the individual patient. Several techniques are used to assess myocardial viability. Nuclear medicine gives reliable information on regional perfusion, metabolism and cell membrane integrity, while echocardiography provides real time visualization of myocardial thickening in basal conditions and continuously during pharmacological interventions. The presence or absence of contractile reserve in akinetic regions can be evaluated by pharmacological stress echocardiography. This article presents the semiology of myocardial viability as characterized by these different methods and reviews their relative value in different clinical settings.