The conduction system of the heart is densely innervated by the autonomic nervous system. The parasympathetic portion of the autonomic nervous system decreases sinus node automaticity and slows AV node conduction and hence decreases the heart rate. On the other hand the sympathetic division can increase the heart rate by increasing the sinus node automaticity and enhancing conduction through the AV node.

The autonomic nervous system functions involuntarily to control motor functions of the heart, lungs, other internal organs and of the smooth muscles of the blood and lymph vessels.

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It is divided into two parts, as follows:

1) the parasympathetic coming from the mid and hind brain and the spinal cord and able to cause constriction of the pupils of the eyes and slowing of the heart rate amongst other functions;

2) sympathetic orginating in the spinal cord and concerned with causing the involuntary response to alarm such as by speeding the heart rate and raising the blood pressure.