Control of blood flow

A blood flow control system comprising a primary arteriovenous fistula (11) having a secondary fistula (14) leading to a venous sink (13) and blood flow control means (15) engaged with the primary fistula (11) between the secondary fistula and the vein whereby restriction of the blood flow through the primary fistula (11) by the blood flow control means increases the flow of blood to the venous sink (11). An implantable device for controlling the flow of blood through a primary arteriovenous fistula (11) so as to control the flow of blood to a venous sink (13) through a secondary fistula (14) connected to the primary fistula (11), comprising inflatable pressure means (50) adapted to engage the primary fistula (11) between the secondary fistula (14) and therein, pump means in communication with the pressure means (50) adapted to inflate the pressure means whereby the pressure means restricts the flow of blood through the primary fistula (11) and means for deflating the pressure means.