Sudden brief loss of conciousness, varying from a few seconds to several minutes. The cause is a reduction in the blood supply to the brain, which is very sensitive to oxygen deficieny; as soon as blood supply is fully restored consciousness returns. Fainting can be caused by violent emotion, very warm surroundings, standing for long periods, anaemia or low blood pressure. If the patient lies flat, possibly with the legs raised, blood pressure rises again and consciousness is quickly restored. Fainting can also be caused by a brief interruption of heart function, usually a break in rhythm so that the heart beats too slowly, and the blood pressure drops. Certain abnormalities of the aortal valve can also cause inadequate blood supply to the brain.