A medical device for placing an embolic device at a predetermined site within a vessel of the body including a delivery catheter and a flexible pusher member slidably disposed within the lumen of the catheter. A fluid pressure source is coupled to the proximal end of the pusher member. An embolic device is retained at the distal end of the pusher member by a mechanical interlocking mechanism. The distal end of the pusher member includes a spiral ribbon section encircled by a tubular member. The tubular member or the distal end of the pusher member directs fluid from the fluid pressure source against the embolic device. The mechanical interlocking mechanism is disengaged from the embolic device and a fluid pressure is applied against the embolic device to ensure the release of the embolic device.