Introduction: Persistence of left superior vena cava (PLSCV) draining into the coronary sinus is a rare con-genital structural anomaly with a prevalence of 0.3%-0.5% of the general population, yet it is one of the most common thoracic venous abnormalities and the most common cause of dilated coronary sinus without left to right shunt. Two types of PLSVC are known in li-terature: in 92% of cases, PLSVC is connected to the right atrium through the coronary sinus without signi-ficant hemodynamic consequences, while in 8% of ca-ses PLSVC connects directly or through the pulmonary veins to the left atrium, causing a systemic-pulmonary shunt

Methods: We present the case of a 57 years old wo-men with patent ductus arteriosus sugically treated at 27 years old and ventricular septal defect operated at 28 years old who presented for a syncopal episode. The patient presented with dyspnea at minimal effort, progressive increase of cyanosis in effort, bradicardia, grade III / VI systolic murmur in left parasternal line and a significant resting desaturation of 84%. Coun-terclockwise 4:1 atrial flutter and right bunddle block are observed. Echocardiography reveales pulmonary hypertension with estimated pulmonary systolic pre-ssure of 65 mmHg, under the condition that the pati-ent had postoperative pulmonary hypertension (mean pulmonary pressure of 60 mmHg at the last cardiac ca-theterization performed at 38 years old). There is no evidence of systemic-pulmonary shunt (Qp / Qs =1) and the presence of dilated coronary sinus 33 mm in diameter is observed.

Results: In the context of echocardiographic changes, the patient undewent cardiac magnetic resonance that showed dilated right atrium with normal right ventricle size and ejection fraction and dilated coronary sinus by loading from systemic venous return through the per-sistence of the left superior vena cava. Cardiac mag-netic resonance did not highlight any communication with right superior vena cava or left-right shunt ele-ments (Qp / Qs =1). At present, the patient is referred for cardiac catheterisation and for electrophysiological study in order to asses the possibility of atrial flutter radiofrequency ablation

Conclusions: Dilated coronary sinus with PLSVC, a rare congenital anomaly, discovered in a patient with surgically treated congenital heart disease history and with residual secondary pulmonary hypertension who had a clinical status depreciation, raised the issue of a residual shunt. In our case, the third congenital ano-maly is not responsible for patient’s pulmonary hyper-tension worsening because it did not cause systemic-pulmonary shunt. On the other hand, the presence of rhythm and conduction disorders, in our case variable atrial flutter, seems to be a frequent association with co-ronary sinus dilation. This anomaly is associated with serious complications in cardiopulmonary bypass and during pacemaker insertion via left subclavian vein-ar-rhythmias, shock, and coronary sinus thrombosis may occur.