Introduction: Pulmonary arterial hypertension (PAH) is a life-threatening complication of uncorrected acyanotic congenital heart disease (CHD). While right heart catheterization (RHC) is the diagnostic gold standard, its invasive nature and limited accessibility in low-resource settings underscore the need for alternative tools. This study aims to evaluate the diagnostic utility of electrocardiography (ECG) markers in predicting PAH severity among children with acyanotic CHD in Bangladesh. Methods & Materials: This cross-sectional analytical study included 83 children (age range: 0.6–17 years) diagnosed with acyanotic CHD at a tertiary care hospital. All participants underwent ECG and cardiac catheterization to assess mean pulmonary artery pressure (mPAP). ECG parameters were analyzed for diagnostic accuracy and correlation with mPAP. Results: PAH was identified in 72.3% of patients, with 40.96% exhibiting severe PAH. R ≥ 7 mm in V1, S ≥ 7 mm in V5, and R V1 + S V5 ≥ 10 mm demonstrated the highest sensitivities (85.0%, 88.3%, and 83.3%, respectively). The composite R V1 + S V5 had the strongest correlation with mPAP (r = 0.68, p < 0.001). All ECG markers assessed showed statistically significant associations with mPAP. Conclusion: ECG parameters—particularly R in V1, S in V5, and their composite—show strong diagnostic value in predicting PAH in children with acyanotic CHD. ECG offers a feasible, cost-effective screening alternative in resource-limited settings.