Single-lead electrocardiogram (ECG) showing first-degree atrioventricular (AV) block I

Electrocardiogram of lead II showing normal sinus rhythm, first-degree atrioventricular block with a prolonged PR interval of 0.30 seconds, and a QRS complex of normal duration. The tall P waves and P wave duration of approximately 0.12 seconds suggest concurrent right atrial enlargement.

Normal rhythm strip in lead II. The PR interval is 0.15 sec and the QRS duration is 0.08 sec. Both the P and T waves are upright.