ectorcardiographic studies of QRS loops in right bundle branch block (RBBB) have been reported by many authors, and the classic abnormalities are discussed in texts and symposium proceedings.l-6 The T loop in RBBB has received scant attention thus far, except for Chou and associates’g who reported the incidence of abnormal T loop wideness in 10 per cent of RBBB cases. The rotational characteristics of T loops in RBBB, as encountered in ischemic heart disease, in right ventricular enlargement, and in healthy persons have not been explored. The purpose of this investigation was to survey T-loop characteristics in a series of patients whose RBBB was of diverse etiology.