An AED will prompt a rescuer when to begin CPR. Depending on the make and model of the AED, most will provide a metronome or beeps to keep you on track for the rate of compressions. Also, some AEDs models provide real-time feedback on the rate and/or depth of compressions. The AED will prompt when to stop compressions for analysis and shock, if needed. Most AED models are programmed to analyze the heart rhythm every two minutes.