It is known that the clotbusting agent (Alteplase), the main effective treatment used in the acute stroke can improve blood flow in already blocked arteries in 50% of patients. However, as it is a powerful drug that dissolves clots, there is a risk that it may cause bleeding (haemorrhage) in the body. This is most serious when it occurs in the brain, either in the region of the stroke or another part of the brain, which if serious, could lead to greater disability or even death. To date, there has been little information regarding the natural history and prognostic significance of impaired cerebral autoregulation during and following restoration of brain blood flow (reperfusion), especially those who received clotbusting agent (Alteplase). There are also conflicting findings between animal and human models. There is evidence from an animal study that restoration of blood flow in postischaemic brain arteries may result in generation of free oxygen radicals, leading to further cerebral autoregulation impairment. Furthermore, there is evidence from animal models that clotbusting agent (Alteplase) may exhibit additional blood vessel toxic effect and therefore, further impair cerebral autoregulation. However, such findings could not be reproduced in the human settings. To date, there is only one small study looking at cerebral autoregulation in 14 acute ischaemic stroke patients 8 days after clotbusting treatment, there have not been studies to assess blood flow regulation at the initiation and completion of the clotbusting treatment.