OBJECTIVES\nTo evaluate serum levels of cardiac troponin I (cTnI), autoantibodies against cardiac troponin (cTnAAbs) and natriuretic peptides during the treatment protocol in children with hypoplastic left heart syndrome (HLHS).\nMETHODS\nIn a prospective study, we had 18 consecutive children with HLHS, for whom serum samples were analysed before the Norwood operation, before the bidirectional Glenn (BDG) operation, at the age of one year and before total cavo-pulmonary connection (TCPC). In addition, we performed a cross-sectional study in 22 children examined before TCPC. Controls comprised 34 healthy children.\nRESULTS\nIn the prospective study, troponin I was positive in eight children before the Norwood operation. At the next follow-up, six children were positive. Thereafter, in all samples, cTnI was negative. Serum levels of natriuretic peptides decreased during the treatment protocol but remained higher than in controls throughout the study. In the cross-sectional study, cTnI levels were negative, but levels of natriuretic peptides were higher than in controls. Levels of cTnI and natriuretic peptides showed no correlation with oxygen saturation or haemoglobin concentration. Autoantibodies against cardiac troponin appeared in one patient but not in the control children.\nCONCLUSIONS\nCardiac TnI release is common before Norwood and BDG operations; then during the treatment protocol for HLHS, cTnI release resolves and serum levels of natriuretic peptides decrease. This may reflect a reduction of volume overload of the right ventricle during the surgical programme.