AbstractBackground and HypothesisInteratrial block (IAB: P‐duration > 100 ms) is poorly recognized in hospital populations. In addition to reduced left atrial function and left atrial enlargement it predicts atrial fibrillation and other arrthymias. P‐terminal force (Ptf): ± biphasic P in lead V1 ≥ area of 1 small square on the electrocardiogram (ECG) grid also indicates left atrial abnormality, particularly left atrial enlargement. These 2 should be related. We determined the intercorrelation.Methods and ResultsTwo blinded observers evaluated 500 consecutive patients' ECGs for both Ptf and IAB utilizing all 12 leads for IAB and V1 for Ptf. Measurement differences were resolved in a consensus conference. Among 482 usable ECGs, IAB and Ptf were strongly and significantly correlated (χ2 = 68.041; P≤.001).ConclusionIAB and Ptf are significantly and strongly correlated and one should be expected in the majority of cases when the other is recognized. Copyright © 2009 Wiley Periodicals, Inc.