A kind of flexible sac with one or more of them being used to apply pressure on an organ or vessel and which functions either for draining fluid from or injecting it into a part of the body for therapeutic purposes: A kind of balloon catheter, with a sausage-shaped balloon, is used to expand narrow arteries which can avoid the need for surgery; although the narrowing of the vessel may occur again.

Another application of the balloon catheter is to treat the bleeding of enlarged veins in the esophagus or stomach, a life-threatening condition of some kinds of liver disease.