Vascular connection between the pulmonary artery and the aorta. Via this connection, the lungs are switched off from the bloodstream before birth. This is done by diverting the blood from the pulmonary artery directly back into the systemic circulation. The connection closes with the newborn's first breaths. If it remains open, blood constantly flows from the aorta back into the lungs. The defect can be corrected surgically or sometimes with medication. Named after the Italian anatomist and physician Leonardo Botallo.