What two mechanisms help the heart recover from excessive vagal stimulation?

The recovery of the heart from excessive vagal stimulation is primarily facilitated by sympathetic reflexes and the initiation of impulses by Purkinje fibers. When the vagus nerve is excessively stimulated, it can lead to a significant decrease in heart rate (bradycardia) and potentially result in hypotensive effects. In response to this situation, the body activates sympathetic reflexes, which involve the release of norepinephrine and other catecholamines that help increase heart rate and improve cardiac contractility. This sympathetic activation counteracts the effects of vagal stimulation.

Additionally, Purkinje fibers play an essential role in the conduction system of the heart. They facilitate the rapid spread of electrical impulses through the ventricles, ensuring that heart muscle contractions are coordinated effectively. This coordination is critical for maintaining an optimal heart rate and can also help restore normal function after excessive vagal activity.

In summary, sympathetic reflexes help restore heart rate and contractility, while the Purkinje fibers ensure effective conduction of the heart's electrical activity, both contributing to the recovery from excessive vagal stimulation.