A second example of an AV nodal re-entrant tachycardia is shown here. It is from a 40 year old male recorded following an appendectomy. He had no history or findings to suggest underlying heart disease and the only abnormality on physical examination was the rapid heart rate. The ECG shows a narrow complex tachycardia with a rate of 185 beats per minute and ST depression in leads II and V5. Note the small deflection at the end of the QRS complex which is present on all leads, but most prominent in lead V1 where it simulates an R’ (arrow). This is the retrograde P wave. The PR interval (the conduction time in the antegrade pathway) is 0.24 seconds and the RP interval (the conduction time in the retrograde pathway) is approximately 0.10 seconds.