Congenital ductus arteriosus aneurysms develop in the third trimester of fetal life, possibly due to abnormal intimal cushion formation or elastin expression in the ductal wall. It is often diagnosed in infants before 2 months of age. Most have a benign course and resolve spontaneously. However, life-threatening complications have been reported. We report a case of large ductal aneurysm diagnosed incidentally in a neonate, in whom there was a novel mutation in the smooth muscle myosin protein gene—MYH11.