What are the complications of a heart attack?

Heart failure ;

When a large amount of heart muscle dies, the ability of the heart to pump blood to the rest of the body is diminished, and this can result in heart failure. The body retains fluid, and organs, for example, the kidneys, begin to fail.

Ventricular fibrillation ;

Injury to heart muscle also can lead to ventricular fibrillation. Ventricular fibrillation occurs when the normal, regular, electrical activation of heart muscle contraction is replaced by chaotic electrical activity that causes the heart to stop beating and pumping blood to the brain and other parts of the body. Permanent brain damage and death can occur unless the flow of blood to the brain is restored within five minutes.
Most of the deaths from heart attacks are caused by ventricular fibrillation of the heart that occurs before the victim of the heart attack can reach an emergency room. Those who reach the emergency room have an excellent prognosis; survival from a heart attack with modern treatment should exceed 90%. The 1% to 10% of heart attack victims who later die frequently had suffered major damage to the heart muscle initially or additional damage at a later time.
Deaths from ventricular fibrillation can be avoided by cardiopulmonary resuscitation (CPR) started within five minutes of the onset of ventricular fibrillation. CPR requires breathing for the victim and applying external compression to the chest to squeeze the heart and force it to pump blood. In 2008, the American Heart Association modified the mouth-to-mouth instruction of CPR, and recommends that chest compressions alone are effective if a bystander is reluctant to do mouth-to-mouth. When paramedics arrive, medications and/or an electrical shock (cardioversion) can be administered to convert ventricular fibrillation back to a normal heart rhythm and allow the heart to pump blood normally. Therefore, prompt CPR and a rapid response by paramedics can improve the chances of survival from a heart attack. In addition, many public venues now have automatic external defibrillators (AEDs) that provide the electrical shock needed to restore a normal heart rhythm even before the paramedics arrive. This greatly improves the chances of survival.