A medical balloon for a balloon pump is disclosed. The medical balloon has a first end and a second end and a port at one of the ends for engaging a catheter for receiving an inflation fluid into the balloon. The balloon has one or more exterior walls defining, when the balloon is inflated at substantially a standard operating pressure, a taper along at least a part of the length of the balloon. The taper has two or more consecutive tapering sections, each tapering section having a different, substantially constant, angle of tapering. The balloon is substantially asymmetrical about a mid-point between the first and second ends when inflated.
