There is confusion over these heart emergencies and it is important to know the difference because all have different cause and treatment.
Heart Attack : A heart attack happens when blood supply of heart muscle is interrupted (blocked). Without getting blood supply (oxygen requirement ) that part of heart begin to die and patient feels chest pain. Depending on how long blood supply was cutoff, the results can be mild damage or it could be massive even fatal. This is a medical emergency and patient should be given Asprin 325 (Chewable tablet) and sublingual Nitroglycerine and rush to near by hospital for further treatment.
Cardiac Arrest : A cardiac arrest happens when the heart suddenly stop beating. It can occur due to multiple reasons including a heart attack or poor heart function. This is a medical emergency that requires immediate medical treatment in the form of Cardiopulmonary Resuscitation (CPR) and may need Automated External Defibrillator (AED). So rush to nearby hospital which is well equipped to deal with such kind of emergencies.

Heart Failure : Heart Failure is a condition in which heart is unable to pump sufficient amount of blood to rest of body parts. It may occurs either due to weak heart or due to onability or heart to relax properly or due to uncontrolled blood pressure. Depending on what is the cause of heart failure , medical treatment is optimized and patient gets relief