what happens when the heart stops
Immediately is about long enough to get one sentence out. Your brain's neurons stop sending signals to each other about 11 seconds after your heart stops. Their death occurs later, maybe even hours later, but they can't send messages to the rest of the body.
A heart attack can cause a cardiac arrest. In cardiac arrest (also called sudden cardiac death or SCD), death results when the heart suddenly stops working properly. This is caused by abnormal, or irregular, heart rhythms (called arrhythmias). The most common arrhythmia in cardiac arrest is ventricular fibrillation.