Eisenmenger syndrome refers to the fact that in congenital heart disease, such as when there is a ventricular septal defect or arteriovenous ductus arteriosus, blood will shunt from the left heart to the right heart in the early stages of the disease because the pressure in the left heart is higher than that in the right heart. As the disease continues to progress, more and more left-to-right shunts will result in higher and higher pressure in the right heart, and in the advanced stages of the disease there will be bidirectional shunts, or even right-to-left shunts, that is, shunts from the right heart to the left heart. The return of blood from the right heart to the left heart causes unoxygenated venous blood to mix with arterial blood, resulting in cyanosis and loss of systolic murmurs, a phenomenon we call Eisenmenger’s syndrome. In Eisenmenger’s syndrome, high right heart pressure, right-to-left shunt, and severe pulmonary hypertension make it a contraindication to surgery, and the prognosis for such patients is poor, requiring combined heart-lung transplantation.