How wide should the PR interval be from the beginning of the P wave to the beginning of the R wave?

The PR interval, measured from the beginning of the P wave to the beginning of the R wave, is an important aspect of interpreting an electrocardiogram (ECG). A normal PR interval typically ranges from 0.12 to 0.20 seconds, which corresponds to 3 to 5 small squares on the ECG paper. Since one large block is equivalent to 5 small blocks, the ideal PR interval should indeed be less than 1 large block—specifically maintaining within the normal range.

This understanding emphasizes the functional connectivity between the atria and ventricles. An interval longer than this could indicate various heart conditions, such as a first-degree heart block, while being too short may suggest other abnormalities. Thus, the correct interpretation aligns the PR interval with the guidelines that it should be less than the width of 1 large block, supporting a healthy conduction system.