The correct answer is D) immediately start CPR. When a person suffers a heart attack and stops breathing, the immediate action required is to begin cardiopulmonary resuscitation (CPR) as soon as possible. CPR is a crucial emergency procedure that can help maintain blood flow and oxygen circulation to the brain and other vital organs until further medical assistance arrives. Prompt CPR increases the chances of survival and recovery for the victim. The other options are incorrect because: A) providing stimulants could be dangerous and worsen the condition, B) making the victim comfortable is not the priority in this emergency situation, and C) administering oxygen alone is not sufficient without performing CPR to restore breathing and circulation.