Fig. 2

Theoretical schematic illustration of circulatory pressure changes. a In a normal biventricular circulation, pressure is generated in the systemic ventricle (LV) to propel flow in the aorta and systemic circulation. The pre-pulmonary pump (RV) provides the pressure to propel flow in the pulmonary artery (PA) which then is distributed in the pulmonary circulation, but this is sufficient to maintain preload in the left atrium (LA). During exercise, the systemic vascular resistance falls such that there is little increase in mean LV pressure requirements. Therefore, a more substantial increase in the RV is required to pump blood anterogradely. b In a Fontan patient, the pulmonary flow is passive due to the lack of a sub-pulmonary ventricle and the flow through the pulmonary circulation depends on the pressure difference between the right atrium (RA) and LA. During exercise, transpulmonary flow can only be augmented by a reduction in pulmonary vascular resistance. (SVC: systemic venous flow, RV: right ventricle, PA: pulmonary artery, PV: pulmonary veins, LV: left ventricle, SV: single ventricle, Ao: aorta)