How do restart somebody's heart?

To restart someone's heart, perform cardiopulmonary resuscitation (CPR) immediately. This involves giving chest compressions at a rate of 100-120 per minute, pushing hard and fast in the center of the chest. If available, use an automated external defibrillator (AED) as soon as possible to deliver a shock that can restore a normal heart rhythm. Always call emergency services for professional medical assistance.