Background: Cor-triatriatum is a rare congenital cardiac abnormality in which left atrium (sinister) or the right atrium (dextrum) is divided into two compartments by a fold of tissue or a fibromuscular membrane. Left superior vena cava (LSVC) is more frequently associated when compared to other anomalies. Due to the rarity of the condition, a high index of suspicion is need to prevent unfavourable outcomes. Case Report: We report a case of 11-year-old male having complaints of exertional dyspnea for 2 months, who underwent surgery for cor-triatriatum. But the membrane was formed by persistent left superior vena cava with dilated coronary sinus which was closely mimicking cor-triatriatum. Conclusion: This case emphasizes about the complexities associated with persistent LSVC, especially in the context of mimicking other congenital cardiac abnormalities.