The parasympathetic effects on the heart are the opposite of the sympathetic system:

It is mediated via acetylcholine receptors located on the SA and AV nodes.

The vagus nerve supplies the heart with parasympathetic fibres. There is a constant vagal tone slowing the heart rate.

If this tone increases, e.g. emotional stress and pain, the heart rate can drop.

When this tone is blocked, e.g. by administering atropine, the heart rate increases.

In addition to a negative chronotropic effect, the parasympathetic system reduces the speed of conduction through the AV node. There are no other significant effects of the parasympathetic nervous system on the heart.