If a Nerve to an Isolated Heart Is Stimulated and the Heartbeat

If a nerve to an isolated heart is stimulated and the heartbeat slows,the most reasonable conclusion is that the heart

A) is responding to a nerve control that inhibits heartbeat.
B) is dying since nerves can only stimulate muscle action.
C) is unaffected by the nerve but responding to some unknown chemical factor.
D) is normal as all nerve stimulation results in decreased muscle activity.
E) None of the choices is correct.