Transthoracic intracardiac lines provide a unique access point for postoperative monitoring and management in paediatric cardiothoracic surgeries, particularly within the single ventricle population where preserving vasculature is crucial for future interventions. This retrospective review examined paediatric single ventricle patients undergoing cardiothoracic surgeries at a tertiary children’s hospital between 2011 and 2018, focusing on the use of and factors associated with transthoracic line complications (infection, thrombosis, malfunction, and migration). A total of 338 lines were placed during the study period, with the majority occurring during palliative surgeries (86.5%). Lines remained in place for a median of 14 days postoperatively. Complications occurred in 21 lines (6.2%), comprising 8 migrations (2.4%), 7 thrombosis (2.1%), 4 malfunctions (1.2%), and 2 infections (0.6%). The presence of a surgical shunt was significantly associated with line complications (odds ratio 2.58, confidence interval 1.05 – 6.31; P 0.03). The use of transthoracic intracardiac lines seems to be safe and should be considered as a primary alternative to other central lines in the single ventricle population. A prospective assessment of transthoracic line complications, along with delineation of unit protocols, may further enhance outcomes in this complex population.