The diagnosis of right ventricular overload is often difficult by the electrocardiogram (ECG) when it is associated with right bundle branch block (RBBB). In this study, we examined the usefulness of the MCG in diagnosis of right ventricular diastolic overload and clarified the features of the magnetocardiogram (MCG) of patients with right ventricular overload with RBBB. In our previous studies, we found that MCG criteria shows higher sensitivity in diagnosis of right ventricular hypertrophy, but the criteria showed higher false positivity in patients with RBBB without any underlying disease (RBBB group). Therefore, we set different MCG criteria for right ventricular diastolic overload (RVO-d) as follows based on the mean +/- 2SD of the RBBB group: 1) R wave at C-3 (Rc-3)greater than or equal to 25 x 10(-12)tesla, 2) S wave at F-4 (SF-4)greater than or equal to 11 x 10(-12)tesla. In patients with a right ventricular pressure of more than 50 mmHg, the MCG criteria showed higher sensitivity and specificity than the ECG criteria. These results suggest that the MCG is useful for diagnosis of right ventricular diastolic overload with RBBB.