Congenital aneurysm of the muscular interventricular septum in association with cardiac arrhythmias and a chromosomal abnormality.

We report a newborn with a congenital aneurysm of the muscular interventricular septum, a conduction system abnormality involving variable left and right bundle branch block, and an abnormality of the short arm of chromosome 20, This combination of anomalies has not been previously reported. To date, the infant has progressed well from a cardiac perspective but has poor muscle tone and developmental delay.