How long will it take my friend to recover from cardiac arrest?

Cardiac arrest: If you mean feel better from the shock of electrical defibrillation, not many days. If you mean from hemodynamic shock, depends on what causes the shock and how quickly it reverses. Assuming the patient survives.

Cardiac arrest: Most importantly, we need to know why he had cardiac arrest. Prognosis depends on the cause and our ability to fix the cause. Does he have coronary artery disease? Again we truly need to know the cause of arrest.