If my memory is correct, it used to be fatal. When the fetus is tiny, and arterial pressures relatively low, there is a communication between the aorta and the pulmonary artery, called the ductus arteriosus.(I think) Ordinarily it involutes before birth. but if it persists the higher pressure in aorta forces blood through it into pulmonary artery which has lower pressure. My brother's only son died of it because heart surgery to correct it had not been developed at that time. So it was fetal, but could often be fatal fifty years ago. Alex, or Doc_Comfort, correct me if I am wrong.

Anybody interested, just type "patent ductus arteriosus" in Yahoo! search box, and up comes a dandy illustration and information about this.