A stroke happens when a blood vessel that supplies the brain gets blocked (ischemic stroke) or ruptures (hemorrhagic stroke). Ischemic strokes account for approximately 80% of all strokes and can be either thrombotic (the clot forms in one of the arteries that supply blood to the brain) or embolic (the clot forms elsewhere in the body and is carried through the bloodstream to the brain). As with heart attacks, time is of the essence in the treatment for stroke. The gold standard treatment for ischemic stroke is tissue plasminogen activator (tPA), which dissolves the clot and restores blood flow, but tPA can only be used within a short period of time (as little as 3 hours) of onset of the stroke. The treatment for hemorrhagic stroke is surgery or other endovascular procedure to stop the brain bleeding.