We investigated the usefulness of QRST isointegral maps (I-maps) for detecting posterior myocardial infarction (MI) with and without conduction disturbance. The I-maps were recorded during sinus rhythm and right ventricular (RV) pacing, which simulated left bundle-branch block (LBBB) in 19 patients with and in 20 patients without MI. Data on 608 normal subjects were used as controls. The "-2 SD area," where the QRST integral value was less than the lower limit of the normal range, was assessed by sigma DM (sum of QRST integral values below the normal range). Posterior MI was diagnosed with a sensitivity of 84%, a specificity of 90%, and a diagnostic accuracy of 87%, assuming that MI was present if sigma DM exceeded 50 mVms. During simulated LBBB, when the criterion sigma DM more than 250 mVms was used, the sensitivity, specificity, and diagnostic accuracy were 79, 75, and 77%, respectively. Thus, I-maps may be useful in detecting posterior MI in patients with and without an intraventricular conduction disturbance.