Background Nodo-ventricular(NV) fiber-related reentrant tachycardias are so rare that most of them were reported by case, while few reports have summarized their common and individual features. Objectives To clarify the electrophysiological mechanism of supra-ventricular tachycardias (SVT) related to concealed NV fibers. Methods and Results We studied the intra-cardiac electrograms during electrophysiological study of 3 cases of SVT concerning concealed NV fibers. Maneuvers including ventricular entrainments, His bundle refractory period ventricular stimuli, adenosine triphosphate injection and so on were done for differential diagnosis before ablation. Among these patients, one had AVNRT with a bystander NV fiber, the other 2 had NV fiber-mediated orthodromic reentrant tachycardias (NVRT). VA dissociation were observed during SVT in all with antegrade His bundle conduction sequence. His bundle refractory period ventricular stimuli reset tachycardias with resetting of the H-H interval advancing the V-V interval, suggesting the existence of an accessory pathway. The cycle length of an NVRT prolonged during the status of functional right bundle branch block. Multiple QRS fusion morphologies during ventricular entrainments on a fixed site could be observed. Conclusions Concealed NV fibers can mediate orthodromic SVT or be a bystander of AVNRT. V-A dissociation usually occur during such SVTs. An NV fiber not only expresses the characteristics of an AP, but also the characteristics of the AV node. Multiple QRS fusion morphologies during ventricular entrainments or His bundle refractory period ventricular stimuli on a fixed site can discriminate NV fibers from NF fibers.