We sought to characterize the electrical activity within the persistent left superior vena cava (LSVC), which normally becomes the ligament of Marshall (LOM) that is known to be related to the genesis of atrial tachyarrhythmias. A 20-pole electrode catheter was used to record the entire activation sequence in the LSVC in a patient with Wolff-Parkinson-White syndrome. Electrical activity representing the musculature of the LSVC could be recorded up to a level as high as the pulmonary artery. Multiple electrical connections between the LSVC and left atrium were shown, and one of the connections exhibited unidirectional conduction block. It might be important to take into account the presence of multiple electrical connections when we consider the LOM as a target for radiofrequency catheter ablation or its role in clinical arrhythmias.