Transitory ischemic attacks (TIA) are caused by blood clots (embolic thrombus) that become stuck in a brain artery. A thrombus can stop blood circulation (ischemia) in an artery. Local ischemia causes symptoms of brain stroke. Symptoms depend upon the brain area supplied by the particular artery. During TIA, the symptoms of a brain insult (stroke) last temporarily because the thrombus is soon dissolved by the fibrinolitic activities of certains enzymes in the blood. Symptoms of stroke will disappear as soon as the thrombus dissolves and blood circulation reestablished. These thrombi usually originate from atherosclerotic plagues in the carotid arteries or from the left atrium or ventricle of the heart. People with atrial fibrillation (a kind of heart arrhythmia) are susceptible for developing thrombi that flow into the arterial circulation and can get stuck in any organ of the body, including the brain (thromboembolia). Thrombi from the carotid arteries always get stuck in the brain.
You can check your father's heart via an ECG and the carotid arteries via acarotid arteriography and doppler image. If there are atherosclerotic plagues found in the carotid arteries, surgery is indicated. Anti-aggregation therapy (aspirin) is also indicated. You can consult a specialist for cardio-vascular diseases and a neurologist to follow up on these diagnostic and treatment procedures.