The leading causes of cerebral injury during cardiovascular (CV) surgery are cerebral blood flow (CBF) insufficiency and embolism. TCD can detect both CBF velocity and micro-emboli in cerebral arteries. However, the middle cerebral artery (MCA) cannot always be detected by the temporal bone approach in elderly Japanese, in whom monitoring of the extra-cranial internal carotid artery (ICA) by the infra-mandible approach is recommended. CBF velocity measured by TCD is useful for cardiopulmonary bypass or selective cerebral perfusion. Most HITS/MES detected by TCD during CV surgery indicate micro-bubbles. However, many micro-bubbles cause cerebral injury. Cerebral protection therapy is needed in case numerous HITS/MES are detected during CV surgery.