Right ventricular obstruction due to anomalous muscle bands.

Subinfundibular obstruction of the right ventricle is a rare congenital cardiac abnormality which has been well described mainly over the past decade. The right ventricle is divided into a proximal high pressure chamber and a distal low pressure chamber. The obstruction is caused by an anomalous muscle bundle or multiple muscle bundles of either abnormal or normal bulbar muscle. Clinical recognition of the defect may be difficult, as it is frequently associated with ventricular septal defects. In I5 cases reported by Fisher et al. (1971) there was an associated ventricular septal defect in 14. Coexisting pulmonary valve stenosis, pulmonary atresia, and persistent ductus arteriosus have all been previously reported to occur infrequently (Gale, Heimann, and Barlow, I969). We report a further two cases without associated ventricular septal defects.