What is patent ductus arteriosus (PDA)?

Patent ductus arteriosus (PDA) refers to a condition where there is an abnormal persistence of the ductus arteriosus, a blood vessel that normally closes shortly after birth. In the fetal circulation, the ductus arteriosus allows blood to bypass the non-functioning lungs by connecting the pulmonary artery to the aorta. If this vessel fails to close after birth, it results in an abnormal circumstance where blood continues to flow between the aorta and the pulmonary artery.

In a normal physiological state, after birth, the ductus arteriosus should close, preventing blood from flowing between these two arteries. However, in PDA, the vessel remains open (patent), leading to a left-to-right shunt. This can result in various complications such as increased workload on the heart and pulmonary circulation.

The other options do not accurately describe this condition. While the normal closure of the ductus arteriosus is important for proper cardiovascular function post-birth, the existence of a patent condition is indeed pathological, which is what makes option C the most appropriate choice in identifying the nature of PDA.