The study aimed to assess whether the 12-lead electrocardiogram (ECG) derived ventricular gradient, a vectorial representation of ventricular action potential duration heterogeneity directed towards the area of shortest action potential duration, can improve ECG diagnosis of chronic right ventricular (RV) pressure load. ECGs from 72 pulmonary arterial hypertension patients recorded <30 days before onset of therapy were compared with ECGs from matched healthy controls subjects (n=144). Conventional ECG criteria for increased RV pressure load were compared with changes in the ventricular gradient. In 38 patients a cardiac magnetic resonance (CMR) study had been performed within 24 hours of the ECG. By multivariable analysis, combined use of conventional ECG parameters (rsr’or rsR’ in V1, R/S>1 with R>0.5 mV in V1, and QRS axis >90°) had a sensitivity of 89%, and a specificity of 93% for presence of chronic RV pressure load. However, the ventricular gradient not only had a higher diagnostic accuracy for chronic RV pressure load by ROC analysis (AUC=0.993, SE 0.004 vs. AUC=0.945, SE 0.021, P<0.05), but also discriminated between mild to moderate and severe RV pressure load. CMR identified an inverse relation between the ventricular gradient and RV mass, but there was no significant relation with RV volume. In conclusion, chronically increased RV pressure load is electrocardiographically reflected by an altered ventricular gradient associated with RV remodeling related changes in ventricular action potential duration heterogeneity. Using the ventricular gradient allows ECG detection of even mildly increased RV pressure load.