The evaluation of dysfunctional, but viable myocardium — and therefore the ability to improve contractile performance with revascularization — in patients with acute or chronic infarction is important for the assessment of the prognosis of the patient and for the planning of further therapeutic strategies. Although the improvement of contractile function at rest after restoration of myocardial blood flow is considered the reference standard for the diagnosis of viability, other points need mentioning. The inner layer of the myocardium contributes most to systolic thickening at rest. Therefore, if the endocardium is necrosed, resting wall motion is unlikely to recover. However, the middle and outer layers of the myocardium contribute more to systolic thickening during stress and, thus, may improve regional and global left ventricular performance during exercise. In addition, a viable rim may contribute to a favorable remodeling process and electrical stability.