Let’s start ECG series: How to diagnose left atrial enlargement on ecg. Best leads to study atrial activity are lead II and V1. Normal width and height of P wave in lead II are less than 2.5 mm each. Width is determined by left atrial activity(it will increase in left atrial enlargement=P mitrale)while height is due to right atrial activity(it will increase in right atrial enlargement = P pulmonale). In V1 normally P wave is biphasic with positive component due to RA and negative due to LA.If LA