What is the diagnosis?

First degree AV block with left atrial overload

The PR interval is 320 msec (normal range: 120 to 200 msec). The negative component of P wave in lead V1 is more than one Ashman unit (1 sq mm or 0.004 mV-sec). Other indices of left atrial enlargement may not be evident in this case. Macruz index will be altered by the prolongation of the PR interval. P mitrale (prolongation of P wave duration with notching of P wave in lead II) may be masked by the P wave merging with the T wave of the preceding cycle.