ascites, accumulation of fluid in the peritoneal cavity, between the membrane lining the abdominal wall and the membrane covering the abdominal organs. The most common causes of ascites are cirrhosis of the liver, heart failure, tumours of the peritoneal membranes, and escape of chyle (lymph laden with emulsified fats) into the peritoneal cavity. In patients having liver disease, the onset of ascites is usually preceded by accumulation of fluid in the ankles. The abdomen is often uncomfortably distended, and muscles become wasted.