A number of changes occur in the electrocardiogram (ECG) of pulmonary embolism. This article deals with the diagnostic value of the newly emerged right bundle branch block (RBBB) as a manifestation of acute right ventricular overload. A certain correlation between the extent of obstruction of the pulmonary artery and the appearance of RBBB is established through dynamic monitoring of the ECG. Fifty cases of dissectionally proven pulmonary embolism are observed, in 20 of which massive trunk obstruction had taken place, and in the remaining 30 peripheral embolism in the pulmonary artery was established. With 80% of the trunk embolism patients (16 cases), a newly emerged RBBB was detected in their ECG, and with the remaining 20% (4 cases), ST-segment depression and T-wave inversion in leads V(1)-V(4) were observed as well as right axis deviation. S(1)Q(3)T(3) syndrome was detected among 60% (12 cases) of trunk embolism patients. In none of the peripheral embolism cases was RBBB in the ECG registered. Thus, its appearance on dynamic monitoring of the ECG of pulmonary embolism patients is a significant sign of the probability of massive obstruction of the main pulmonary trunk.