The other treatment involves the amount of CPR given before the emergency medical services (EMS) providers first look at the heart rhythm to determine if a shock is needed. A person would receive either about 30 seconds of chest compressions or about 3 minutes of compressions before checking the heart rhythm. Giving some compressions before checking the heart rhythm increases the blood being circulated to the body. Researchers do not know how many compressions before the rhythm check are necessary to save more lives.