A First Degree AV heart block is just about always asymptomatic.
It is an EKG finding of a prolonged PR segment. A normal PR interval is from 120-200 msec, and a PR interval on the EKG to more than 200 msec is diagnostic, as well as, definitive.
A first degree AV block can arise from delays in the conduction system in the AV node, the His-Purkinje system, or a combination thereof. (5)

It is a result of a delay in the signal from the atria to the ventricles in the heart. It can be thought of as an abnormality of the spread or flow of electrical activity from the upper heart chambers, the atria, to the lower heart chambers, the ventricles.

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