Final answer:
The effect of acetylcholine on muscarinic receptors in the heart is typically inhibitory, as it tends to hyperpolarize cardiac muscle cells and slow the heart rate.
Step-by-step explanation:
The effect of acetylcholine on muscarinic receptors in cardiac muscle cells can be either inhibitory or excitatory, depending on the subtype of the receptor. In the heart, these receptors typically work to slow down the heart rate through hyperpolarization, which is an inhibitory action. Acetylcholine binding to muscarinic receptors on cardiac muscle cells generally causes an increase in potassium efflux, leading to hyperpolarization of the cell membrane, thereby slowing the heart rate and exerting an inhibitory effect on cardiac function.