Changes in the spatial ventricular gradient (VG) in Frank lead vectorcardiograms after the treadmill exercise test were examined for the purpose of clarifying primary ST, T changes accompanying complete right bundle branch block (CRBBB). The subjects consisted of 20 healthy controls, 21 isolated CRBBB patients, 52 ischemic heart disease (IHD) patients with normal ventricular conduction and 16 IHD patients with CRBBB. In healthy controls and isolated CRBBB patients, the magnitude of the VG decreased after exercise. Few changes were observed in the azimuth and elevation. In IHD patients, regardless of whether they had CRBBB or not, the magnitude of the VG at rest was less than in controls, and the VG deviated from the ischemic area. After exercise, changes in the azimuth and elevation were significantly larger in IHD patients, regardless of having or not having CRBBB, than in controls. Post-exercise changes in the VG azimuth of more than 20°, and VG elevation of more than 15°, provided high sensitivity and specificity for detecting IHD associated with CRBBB. Tokunaga divided patients with CRBBB into two groups. In group A, the duration of the S wave from lead Ⅱ in standard 12-lead electrocardiograms (ECG) was equal to or larger than 0.08 sec, while in group B, it was equal to or less than 0.08 sec. In the present study, patients with lesions of the left anterior descending artery belonged to group A, while those with lesions of the right coronary artery belonged to group B. The ST-segmest depression in lead X or Y in Frank lead scaler ECGs had a sensitivity rate of no more than 50% in detecting coronary artery disease in the presence of CRBBB. The ST depression limited to lead Z gave a high false positive rate.