Well, they're "similar" in the sense that they both have to so with your heart, but a heart attack can lead to cardiac arrest.

Then again, there's many things that can happen with your heart that don't necessarily involve it stopping... You could go into fibrillation (Atrial or ventricular), and that can cause your heart to stop pumping blood, but continue to "try" (the rhythm isn't effective in keeping blood flow).

The heart can be pretty interesting, along with the rest of your body...