INTRODUCTION: Persistent left superior vena cava (PLSVC) is a congenital vascular anomaly that is often asymptomatic and typically discovered incidentally. In this case, the patient had a known cardiac anomaly, and PLSVC was diagnosed following radiological suspicion. CASE: A 38-year-old female patient was evaluated for chronic exertional dyspnoea. Chest radiography revealed enlargement of the upper and anterior mediastinum. Contrast-enhanced thoracic computed tomography confirmed the presence of PLSVC. Echocardiography showed that the PLSVC drained into the right atrium via an enlarged coronary sinus. The patient was also being followed for an atrial septal defect, cardiomyopathy, and an interatrial septal aneurysm. Additionally, she was diagnosed with asthma, and appropriate treatment was initiated. CONCLUSION: Enlargement of the upper and anterior mediastinum on chest radiography, the presence of a dilated coronary sinus on echocardiography, and/or associated congenital cardiac anomalies should prompt consideration of PLSVC. Recognising this anomaly prior to invasive procedures is critical, as it may lead to unexpected complications.