Introduction: Inferior vena cava (IVC) congenital anomalies are relatively rare vascular anomalies that are detected accidentally by imaging during the diagnostic treatment of deep vein thrombosis or more frequently, by treating non-vascular pathology. (1-3)

Case report: A twenty-seven-year-old patient was hospitalized at the Department of Cardiology of University Hospital “Merkur” for electrophysiological treatment (EPI) due the diagnosis of inappropriate sinus tachycardia (IST) after previously excluded reversible factors of sinus tachycardia and postural orthostatic hypotension. Electrophysiologic study was initiated, but due to unexpected anomalies of the venous system, the same was not done in that act. A MSCT described the duplication of IVC with the continuation of the hemi-azygos veins of the left IVC and the successive right-sided May-Thurner syndrome for which an anticoagulant therapy was initiated, and a thrombophilia test was performed. The patient is homozygous for polymorphism C667T and polymorphism A1298C. In the second act, EPI was performed, confirming the IST and in the same act the sinus node therapeutic modification was done.

Conclusion: Left-sided IVC cases associated with congenital heart defects are not often described, and IST has never been described as a possible consequence of venous system malformation. The sinus node is a spinal sub-epicardial specialized muscular structure located postero-laterally within the epicardial groove of the right atrial terminal sulcus, at the junction of the trabecular frontal attachment and the smooth-walled muscular venous component posterior. On the epicardial side, it is placed on the attachment of the superior vena cava with a right atrium and continues down and down the sulcus terminalis and ends subendocardially near the IVC. Localization and embryological development are in favour of the same etiologic factor that has led to an anomaly of IVC and sinus node dysfunction.