A heart attack happens when blood supplying the heart muscle is cut off due to a clot in one of the coronary arteries. This can cause chest pain, although symptoms can be less severe, and can permanently damage the heart. The heart is still sending blood to the body and the person will be conscious and breathing. A person having a heart attack has a high risk of experiencing a cardiac arrest.
A cardiac arrest occurs when the heart suddenly stops pumping blood around the body, often because of a problem with the electrical signals to the heart muscle. Someone who is having a cardiac arrest will suddenly collapse and will stop breathing.
Both a heart attack and a cardiac arrest are life-threatening medical emergencies 
