Rationale. Better understanding of the early stages of RV dysfunction in two poorly understood patient groups with poor prognosis; repaired tetralogy of Fallot (ToF) and Mustard repair of TGA (Mustard), is needed. Objectives. This study aimed to characterize neurohormones and oxidative stress (aldehydes) in ToF and Mustard patients with isolated RV dysfunction. Methods. 93 congenital cardiac patients were recruited from the TGH. The levels of the following biomarkers were compared to levels in control subjects; ANP, BNP, ET-1, Ang-11, MDA, 4-HNE, hexanal, and heptanal. Clinical parameters including, NYHA class, RV function and size were evaluated for correlations to the biomarkers. Results. ANP, BNP, hexanal, and heptanal were significantly elevated in both congenital cardiac groups. These paramenters also correlated significantly to NYHA class. Discussion. ANP and BNP can be activated by RV volume overload (ToF) or pressure overload (Mustard). Oxidative stress needs to be further evaluated in these two patient populations.