Introduction: Infants and children with congenital heart disease (CHD) are considered physiologically vulnerable to stressors such as fever, tachycardia, and hypotension following vaccination. The Sri Lankan Ministry of Health recommends inpatient vaccination with close observation for selected high-risk cardiac conditions. Objectives: To assess adherence to national guidelines on post-vaccination observation in children admitted with congenital or suspected cardiac disease and to describe adverse events following immunisation (AEFI). Methods: A retrospective clinical audit was conducted among children admitted for postvaccination observation in a district general hospital Galle from 01/12/2025 to 31/01/2026, Sri Lanka. Audit standards were derived from the Ministry of Health General Circular No. 01-26/2012. Results: Seventeen children were included. Sixteen (94.1%) were observed for ≥24 hours. Adverse events were observed in 29.4% of children, predominantly fever. No serious cardiovascular instability , ICU admission, or mortality occurred. Conclusion: Although observation duration was high, a significant proportion of admissions did not strictly meet national criteria. Post-vaccination adverse events were mild and self-limiting.