To characterize "normal electrocardiogram patterns" after transplantation, serial surface 12-lead electrocardiograms (ECGs) taken 2 weeks, 1 month, and 1 year postoperatively in a group of 50 heart transplant recipients were analyzed and were correlated with clinical parameters. Some recipient atrial activity was evident in 40% of patients at 2 weeks, but in only 16% at 1 year; donor atrial activity was normal in 90% to 94% of patients at all times. ECG intervals generally were normal and did not change over time. The most prevalent abnormality was the presence of incomplete (IRBBB) or complete right bundle branch block (RBBB) patterns (14% at 2 weeks, 16% at 1 month, and 22% at 1 year). In patients with hemodynamic measurements available approximately at the time of the ECG recording 1 year following transplantation, there was a significant correlation between the presence of IRBBB and RBBB patterns and somewhat higher levels of right atrial mean pressure (6.8 versus 3.9 mm Hg, p = 0.01), pulmonary artery systolic pressure (32.5 versus 24.5 mm Hg, p = 0.001) and diastolic pressure (16.2 versus 11.2 mm Hg, p = 0.004), and right ventricular systolic pressure (31.4 versus 26.9 mm Hg, p = 0.019) and pulmonary artery wedge mean pressure (11.3 versus 7.9 mm Hg, p = 0.010). Repolarization changes were also common but decreased in frequency over time (78% at 2 weeks to 34% at 1 year) and did not correlate with the presence or absence of rejection. We conclude that ECG abnormalities in heart transplant recipients are generally mild and that IRBBB and RBBB patterns correlate with increased right heart pressures.