The early postoperative period in infants following the correction of congenital heart defects is often accompanied by hemodynamic lability, systemic stress, and an acute-phase response, which may lead to transient organ dysfunction, particularly renal impairment.

Aim. To determine the phenotypes of early postoperative complications and the pattern of laboratory responses in infants after cardiac surgery.

Material and methods. A retrospective analysis of 101 infants aged 1 to 12 months who underwent cardiac surgery was performed. Postoperative complications were categorized using a syndromic (phenotypic) approach. Laboratory parameters before and after surgery were compared using a paired t-test; differences were considered statistically significant at p < 0.05.

Results. The profile of early postoperative complications was predominantly characterized by the cardiohemodynamic phenotype (94.06 %). A pulmonary vascular component was observed in 8.91 % of the patients and acted as a clinically significant modifier of the disease course. Conduction disturbances requiring pacing occurred in 2.97 %, and pericardial complications in 0.99 %. Laboratory dynamics corresponded to a triad of systemic changes: anemia / hemodilution (decreased hemoglobin and red blood cell count), a stress and acute-phase response (neutrophilia, lymphopenia, elevated erythrocyte sedimentation rate, and increased C-reactive protein), and renal stress (elevated creatinine with a trend toward increased urea). These pre- and postoperative differences were predominantly statistically significant (p < 0.05).

Conclusions. The leading early postoperative phenotype in infants after congenital heart defect correction is cardiohemodynamic instability (ICD I50.*; 94.06 %), which, in a subset of patients, co-occurs with a pulmonary vascular component (ICD I27.*; 8.91 %) and a laboratory triad of systemic responses (anemia / hemodilution, acute-phase reaction, and signs of renal stress). These findings support the prioritization of hemodynamic and perfusion control, alongside context-based monitoring of inflammatory markers and renal function, during the first 24–48 hours after surgery.