A fifty-six-year-old woman was admitted to Osaka Rosai hospital because of dyspnea, chills, and fatigue. The patient was diagnosed by transthoracic echocardiography as having congestive heart failure due to severe biatrioventricular valve regurgitation, and cardiac surgery was proposed. Preoperative transesophageal echocardiography (TEE) revealed a dilatation of the coronary sinus (CS), a right-sided hemiazygos vein (R-AZ), and another great vessel lying between the CS and the R-AZ. Magnetic resonance imaging (MRI) was also performed, and this showed a persistent right superior vena cava (PRSVC) entering the left atrium via the dilatated CS. However, the site of connection between the R-AZ and the PRSVC could not be detected by MRI because of inadequate slice acquisition. Each method has its limitations, particularly with regard to visualizing the extracardiac vascular system. Therefore, the authors demonstrated that the combination of TEE and MRI might be more useful than each alone, and the combination is as a valuable method as digital subtraction angiography for the diagnosis of extracardiac venous anomalies.