A condition of short duration that starts quickly and has severe symptoms. It may also refer to a symptom; for example, severe pain. An ‘acute’ abdomen is a serious disorder of the abdomen requiring urgent treatment, usually surgery. Acute heart failure is the sudden stopping of, or defect in, the action of the heart. Acute LEUKAEMIA is a rapid growth in the number of white blood cells, which is fatal if untreated. (Opposite: chronic – see CHRONIC DISORDER.)