The PR interval is the time from the beginning of the P wave (atrial depolarization) to the beginning of the QRS complex (ventricular depolarization). The normal PR interval measures 0.12-0.20 seconds ...

A first-degree AV node block occurs when conduction through the AV node is slowed, thus delaying the time it takes for the action potential to travel from the SA node, through the AV node, and to the ...