obstructing blood flow from the right ventricle to the pulmonary artery) Overriding aorta (aortic valve is enlarged and appears to arise from both the left and right ventricles instead of the left ventricle, as occurs in normal hearts) Right ventricular hypertrophy (thickening of the muscular walls of the right ventricle, this is a result of the increased amount of work the heart has to do) Ventricular septal defect (a hole exists in the septum that divides the left and right ventricles) Outside of heart-related conditions, right-to-left shunts of the heart can be seen with Pulmonary Arteriovenous Malformations (PAVMs). Symptoms Early cyanosis is a symptom of a right-to-left shunt. A right-to-left shunt results in decreased blood flow through the pulmonary system, leading to decreased blood oxygen levels (hypoxemia). Hypoxemia manifests as cyanosis, causing "blue babies." Diagnosis Differentiation between a right-to-left shunt and pulmonary disease is often aided clinically by the results of a hyperoxia test. Using high levels of inspired oxygen should have little effect on the dissolved O2 in the blood because highly oxygenated blood is diluted by shunted (low oxygenation) blood. Shunt equation Qs/Qt is the shunt fraction CcO2 is the end-capillary oxygen content CaO2 is the arterial oxygen content CvO2 is the mixed venous oxygen content. Reptiles Because most reptiles have a single ventricle and all reptiles have both a right aortic arch and a left aortic arch, all reptiles have the capacity for right-to-left shunt. References Medical terminology