What effect does parasympathetic activation have on the heart?

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The firing rate of the SA node slows downThe AV node becomes more excitableContraction strength of the ventricles diminishesHeart rate speeds up

Explanation

Parasympathetic stimulation primarily reduces the heart rate by decreasing the firing rate of the sinoatrial (SA) node. It does not enhance AV node excitability, reduce ventricular contraction directly, or cause tachycardia.