During the first 3 - 6 hours after the start of the heart attack are very critical. In the first few hours the person will experience arrhythmias and if taken to the hospital to seek professional help the arrhythmias can almost always be stopped and hopefully saving the person from severe damage. Another crucial thing that needs to be done within the first few hours is for the blockage in the artery needs to be opened so that oxygen can resume its path to the heart and trying to save you from permanent damage. The magic number is usually 6. After 6 hours without medical treatment your risks greatly increase and the chance for death is extremely high otherwise permanent damage.