Coronary sinus catheterization requires an approach into the right atrium via the superior vena cava. This study contains information regarding a coronary sinus long sheath catheter (CS sheath) system, a new device for cannulation of the coronary sinus through the femoral approach. This method was successful in 96.9% of the cases attempted. Furthermore, cannulation using the CS sheath allowed us not only to insert several catheters into the coronary sinus for clinical use and investigation, but also to access the great and small cardiac veins easily and selectively.