Smadja DM et al (Circulation. 2009;119:374-381) from Paris Descartes University has suggested that circulating endothelial cells may be a new biomarker for irreversible pulmonary hypertension in congenital heart disease. This is because irreversible pulmonary hypertension in congenital heart disease is associated with endothelial damage and increased circulating endothelial cell count. Surgical lung biopsy specimens in their study showed endothelial remodeling in irreversible pulmonary hypertension but not in reversible pulmonary hypertension. In their study they looked for circulating endothelial cells and circulating progenitor cells in peripheral venous blood, pulmonary arterial blood and pulmonary venous blood of 26 patients. The numbers of circulating progenitor cells were not different between those with reversible and irreversible pulmonary hypertension.