ductus arteriosus (duk-tŭs ar-teer-i-oh-sŭs) n. a blood vessel in the fetus connecting the pulmonary artery directly to the ascending aorta, so bypassing the pulmonary circulation. It normally closes after birth. patent d. a. (PDA) failure of the ductus to close, producing a continuous murmur and consequences similar to those of a septal defect.

ductus arteriosus A channel that connects the pulmonary artery with the aorta in the mammalian fetus and therefore allows blood to bypass the inactive lungs of the fetus. Derived from the fifth aortic arch, it normally closes soon after birth.