A patient suddenly can't speak and the right side goes weak; CT shows no bleed. The left middle cerebral artery — a branch of the internal carotid — is blocked: an ischemic stroke. Brain tissue dies within minutes without blood, so 'time is brain.' Because no hemorrhage is seen, clot-busting drugs can be given within 4.5 hours to dissolve the clot. The left-brain lesion explains right-side weakness and speech loss (both controlled by the left hemisphere in most people).