This study aimed to assess pulmonary functions before and after cardiac surgery in infants with congenital heart diseases and pulmonary overflow and to clarify which echocardiographic parameter correlates best with lung mechanics. Between 2008 and 2009, 30 infants with left-to-right shunt congenital acyanotic heart diseases who had indications for reparative surgery of these lesions were assessed by echocardiography and infant pulmonary function tests before the operation and 6 months afterward. Tests using baby body plethysmography were performed to assess the following infant pulmonary functions: tidal volume, respiratory rate, respiratory system compliance (C _rs) and respiratory system resistance, functional residual capacity (FRC), and airway resistance. The mean age of the patients was 10.47 ± 3.38 months, and their mean weight was 6.81 ± 1.67 kg. Ventricular septal defect and combined lesions were the predominant cardiac diseases (26.7 %). Comparison of the infant pulmonary function tests showed a highly significant improvement in all the parameters between the preoperative and 6-month postoperative visits (p < 0.0001). Systolic pulmonary artery pressure had a statistically significant negative correlation with C _rs (r = −0.493, p = 0.006) and a positive correlation with FRC (r = 0.450, p = 0.013). The findings showed that C _rs had a statistically significant negative correlation with the pulmonary artery size (r = −0.398, p = 0.029) and the left atrium size (r = −0.395, p = 0.031), whereas the pulmonary artery size had a statistically positive correlation with effective resistance (r = 0.416, p = 0.022) and specific effective resistance (r = 0.604, p = 0.0001). Surgical correction of left-to-right shunt congenital heart diseases had a positive impact on lung compliance, airway resistance, and FRC. Noninvasive echocardiographic parameters assessing pulmonary vascular engorgement and pulmonary artery pressure were closely related to these infant pulmonary function test indexes.