Stroke is a type of cerebrovascular disease that involves the vessels of the central nervous svstem. It usually occurs with sudden onset due to a burst of cerebral arteries, hemorrhage or occlusion by a thrombus or other particles ischemia, leading to focal brain dysfunction. Immediately, nerve cells depleted of oxygen in the involved vascular territory will be functionally disturbed and die if the circulation is not promptly restored. Two main mechanisms leading to ischemic stroke are occlusion and hemodynamic impairment. These two situations decrease the cerebral perfusion pressure and eventually lead to cellular death. The brain blood flow can be maintained by autoregulation of cerebral arteries and collateral circulation within certain limits. When occlusion of an artery develops, blood flow in the periphery of the infarct core is usually reduced but still sufficient to avoid structural damage, so that the functional modifications of cells may be reversible if circulation is restored. This ring-like area of reduced blood flow around the ischemic center of infarct has been termed penumbra as an analogy of the half-shaded part around the center of a solar eclipse. It may largely explain the functional improvement occurring after stroke. Indeed, the neurons surviving in this critical area of infarct at reduced blood flow may again ftunction as soon as blood flow and oxygen delivery is restored.