When the heart stops, cardiopulmonary resuscitation (CPR) should be performed immediately. The following are the specific steps:

Check awareness and breathing: Gently shake the patient's shoulders and call their name loudly to see if there is a response. Also check the patient's breathing to see if there is breathing or only intermittent breathing.

Begin chest compressions: Place the patient on a solid floor in the supine position, and unbutton the coat and belt. Kneel next to the patient, overlap the heels of your hands and place them above the center of the sternum. Make sure your shoulders, elbows and wrists are vertical. Press with your body weight to a depth of 5 to 6 cm at a frequency of 100 to 120 times per minute. This can simulate the pumping function of the heart and help blood flow to various organs throughout the body.

Perform artificial respiration: After every 30 compressions, perform two artificial respirations. Tilt the patient's head back, pinch their nose, and breathe mouth-to-mouth or through a mask, each breath lasting 1 second. Make sure the patient's chest rises when you insufflate.

During the entire first aid process, the patient's reaction should be continuously observed, and the emergency telephone number should be called as soon as possible to request assistance from professional medical personnel.

In addition, if an automated external defibrillator (AED) is available on site, the AED should be used for monitoring as soon as possible. An AED can detect the heart's rhythm and deliver an electric shock to restore a normal heart rhythm if needed.

It should be noted that cardiopulmonary resuscitation is an emergency and professional first aid measure. It is very important for non-professionals to receive relevant training and master the correct operation methods. When administering first aid, stay calm, follow the steps, and seek professional medical help as soon as possible.

In short, cardiac arrest is an emergency and requires immediate first aid measures such as cardiopulmonary resuscitation. Correct operating methods and timely medical assistance are crucial to saving patients' lives.