Background: Patients with strong pulmonary vascular occlusive lesions are at risk of developing postoperative pulmonary hypertension (PH). We aimed to evaluate preoperative right ventricular (RV) function in patients with ventricular septal defect (VSD) who required cardiac surgery during infancy and consequently developed postoperative PH and to determine whether we could preliminarily evaluate postoperative PH in these patients. Methods: We retrospectively analyzed 55 infants with VSD who underwent cardiac surgery between March 2014 and April 2020. We evaluated the measurements of preoperative general function and 2D strain between these two groups: a group with postoperative PH (post-PH, n=10) and a group without postoperative PH (post-NPH, n=45). Results: Post-PH patients had a significantly lower tricuspid annular plane systolic excursion (TAPSE) (11.1 mm), TAPSERA (the proportion of TAPSE due to right atrial (RA) contraction alone) (7.0 mm), RA ejection fraction (36.1 %) and RA expansion index (56.4 %) than the post-NPH patients. Furthermore, the post-PH group had a significantly lower peak RA longitudinal strain (PRALS) (32.0 %) than the post-NPH group (43.0%). Multivariate logistic regression model demonstrated that PRALS was independent echocardiographic parameters for the presence of post-PH (OR 1.18, 95% CI: 1.02 - 1.36, p = 0.03) . The sensitivity and specificity of predicting post-PH for ≤ 35 % of the PRALS were 88.9 % and 70.0 %, respectively, with an area under the curve of 0.85 (p < 0.01). Conclusion: RA parameters demonstrated preoperative RV diastolic dysfunction in the post-PH group. PRALS could be useful factors for predicting postoperative PH.