Sudden cardiac arrest and heart attacks are different:

Different symptoms

A heart attack and SCA produce different symptoms in their victims.

Sudden Cardiac Arrest:

• Collapse and loss of consciousness
• Loss of pulse and blood pressure;
• Cessation of normal breathing; and
• Unresponsiveness

Heart attack:

• Uncomfortable pressure, fullness, squeezing, or pain in the center of the chest lasting more than a few minutes
• Pain spreading to the shoulders, neck, or arms
• Chest discomfort with lightheadedness, fainting, sweating, nausea, or shortness of breath
• Atypical chest pain, stomach, or abdominal pain
• Nausea or dizziness
• Shortness of breath and difficulty breathing
• Unexplained anxiety, weakness, or fatigue
• Palpitations, cold sweat, or paleness

Different causes

Heart attack (or myocardial infarction): occurs when a blockage slows or stops blood flow to some part of the heart muscle. If the blockage is severe or if it is left untreated, that part of the heart muscle can die. Heart attacks do not necessarily cause cardiac arrest or sudden cardiac death, although those conditions could result.

Sudden cardiac arrest: usually the result of a congenital abnormality, but can result from a blow to the chest, a phenomenon called commotio cordis

Different treatment 

CPR may be an effective treatment for a heart attack until paramedics arrive

CPR is not effective for an SCA victim, for whom early defibrillation with an AED is essential, and the most important link in the Cardiac Chain of Survival