Abstract: A balloon catheter system comprising one or more conduits to which are attached a compliant balloon 84 having a non-helical shape in its deflated state, wherein said balloon is constructed such that is capable of adopting a spiral or helical conformation upon inflation, and wherein the external diameter of the spiral or helical balloon thus formed is in the range of 6-15 mm. The balloon catheter system of the present invention may be used for improving the perfusion of cardiac tissues in a mammalian subject, by means of inflating said balloon within the coronary sinus such that it adopts a spiral conformation, thereby causing partial occlusion of said coronary sinus and causing an elevation of coronary sinus pressure.