Abstract
<title>Abstract</title> <p> <bold>Background:</bold> Unroofed coronary sinus (URCS) is an exceptionally rare congenital cardiac anomaly, accounting for less than 1% of atrial septal defects (ASD). It results from partial or complete absence of the common wall between the coronary sinus and the left atrium, producing a left-to-right shunt. URCS is usually associated with a persistent left superior vena cava (PLSVC); the absence of PLSVC, as in the case described here, is a rarer variant. Because presentation is often nonspecific, diagnosis is frequently delayed and requires advanced multimodality cardiac imaging. <bold>Case presentation:</bold> A 50-year-old male ex-smoker presented with a three-month history of palpitations and exertional breathlessness, with a prior syncopal episode. Transthoracic echocardiography demonstrated a 20–22 mm coronary sinus-type ASD due to unroofing of the superior wall of the coronary sinus, left-to-right shunting, severe right atrial and ventricular dilatation, and a bicuspid aortic valve with moderate regurgitation; left ventricular ejection fraction was preserved at 55%. Chest radiography showed cardiomegaly, hilar congestion, and dorsal scoliosis. The patient underwent aortic valve replacement with a 23 mm mechanical bileaflet prosthesis and ASD closure using an autologous fenestrated pericardial patch, with an uneventful early recovery. Two months postoperatively he developed atrial flutter, which was successfully terminated with electrical cardioversion, restoring sinus rhythm. <bold>Conclusions:</bold> This case, classified as Type II URCS (unroofed coronary sinus without PLSVC), illustrates the diagnostic value of transthoracic echocardiography in an entity that is easily overlooked, and supports individualised surgical planning, including fenestrated patch closure in patients at risk of elevated right-sided pressures, together with structured long-term follow-up for late arrhythmic complications. </p>