How Significant is First Degree Heart Block?

First degree heart block is an abnormality in the electrical conduction of the heart noted on the ECG, the recording of the electrical activity of the heart. It is not a block in the blood vessels of the heart which we are more familiar with. The waves on an ECG are P, QRS complex and the T wave.
Normal interval between the onset of the P wave and the onset of QRS complex is up to one fifth of a second (0.2 seconds). When this interval is increased, it is called first degree heart block or first degree atrioventricular or AV block to be specific. Atria are the upper chambers of the heart and ventricles the lower chambers.
This interval is known as the PR interval. PR interval is the time taken for the electrical activity to travel from the upper chambers to the lower chambers. Most of it is due to a delay produced in the atrioventricular or AV node at the junction between the upper and lower chambers.