Hypothesis: We hypothesized that a single regimen of no or limited diuretics post-discharge after pediatric cardiac surgery for patients with two ventricles is not inferior to prolonged diuretics for prevention of readmission for pleural effusion.Material and Methods: A prospective, one-armed, safety non-inferiority trial with historical controls was performed at a single center, quaternary, children's hospital. Inclusion criteria were children aged 3 months to 18 years after pediatric cardiac surgery resulting in a two-ventricle repair between 7/2020 and 7/2021. Eligible patients were compared with patients from a ve-year historical period (selected using a database search). The intervention was that "regular risk" patients received no diuretics and pre-speci ed "high risk" patients received ve days of twice per day furosemide at discharge.Results: 61 subjects received the intervention. None were readmitted for pleural effusions, though 1 subject was treated for a symptomatic pleural effusion with outpatient furosemide. The study was halted after an interim analysis demonstrated that 4 subjects were readmitted with pericardial effusion during the study period versus 2 during the historical control (2.9% versus 0.2%, p = 0.003).Conclusions: We found no evidence that limited post-discharge diuretics results in an increase in readmissions for pleural effusions. This conclusion is limited as not enough subjects were enrolled to de nitively show that this strategy is not inferior to the historical practice. There was a small, but statistically signi cant, increase in readmissions for pericardial effusions after implementation of this study protocol.