An abnormality of body fluids that may occur for many reasons. For example, after heart surgery that involves cardiopulmonary bypass, it is common for the individual to retain large quantities of fluid for several days (causing marked swelling of the body). Children may show symptoms of fluid imbalance from diarrhea. Replacing the fluid is important, but may require medical supervision. It is important to replace fluids adequately, but not overhydrate the child. There are many illnesses that may involve symptoms of fluid imbalance. The key is to seek medical attention when signs of dehydration or swelling take place, in order to prevent more serious complications.