What is the difference between sudden cardiac arrest (SCA) and a heart attack?

A heart attack is a condition in which a blood clot suddenly blocks a coronary artery, resulting in the death of the heart muscle supplied by that artery, unless the clot is opened within a few hours. Heart attack victims usually experience symptoms such as chest discomfort or pain and remain conscious. Most people who have a heart attack survive the event. Other people have an Sudden Cardiac Arrest (SCA) independently from a heart attack and without warning signs. SCA results in death if it is not treated immediately.