If you are in cardiac arrest, is your heart motionless or quivering?

Either: Cardiac arrest just means the heart is not functioning effectively as a pump. Sometimes there is chaotic electrical activity causing it to "quiver" this is ventricular fibrillation. There are other situations in which the heart is motionless, perhaps without any electrical activity at all ( asystole) or with activity bit no contractions ( pulseless electrical activity).

Possibly either: Strictly speaking cardiac arrest means no electrical activity in the heart or what is called asystole. However, effective pumping of the heart also ceases in ventricular fibrillation where the heart would be quivering, but unable to pump blood.

Could be either..: During cardiac arrest, the heart is not beating effectively to deliver blood to the tissues. It could be quivering if the heart is in ventricular fibrillation rhythmn or it could be completely still if the rhythmn is asystole. Either way, the person would have no pulse. A heart monitor is needed to tell the difference.