Premature babies are affected by a condition known as "patent ductus arteriosus" in which the ductus arteriosus (a normal structure) fails to close after birth as it should. A very large ductus can put extra strain on the heart and lungs, making the baby's breathing dependent on a mechanical ventilator. Attending physicians can close the duct with medical\or surgical treatment but assessing whether this is justified can be difficult. The physician usually bases this decision on assessment of the baby's general condition and an ultrasound evaluation of the heart (called an "echocardiogram") but the last is particularly dependent on availability of skilled operators.