The 4 main functions of the human heart are to maintain your blood pressure, pump oxygenated blood through your body and to your brain, pump hormones as well as well as vital nutrients and substances to parts of your body that needs it.
And also the hearts other main function is to receive deoxygenated blood and carry metabolic waste products from the body and pumping it to the lungs for oxygenation.
Without your heart pumping the blood you cannot survive.
That is why if your heart stops it's important to get the heart restarted as soon as possible if possible.
If the heart fails to pump and the brain does not get the oxygen it needs then the brain cells die off and even if you were to get the heart started the person could still suffer brain damage if the heart is not started again soon enough.
So if you think you or someone may be about to have a heart attack get to the emergency room or call 911 as it's better to have the ambulance and medical services to you in time and not need them than not call and not be able to get them to you.