The HeartSine 450P has all the same great features and benefits as the 350P/360P with the added benefit of CPR Rate Advisor. The CPR Rate Advisor gives audible and visual guidance to assist the rescuer in performing CPR at the proper rate. The AED will announce if the rescuer needs to push faster, push slower, or "good speed" if the rate is correct. The CPR rate gauge on the 450P gives real-time visual guidance on the rate of compressions. For just a little more money, you get a built-in CPR coach!