Implantable cardiac monitors (ICM) are valuable tools for syncope's and arrhythmia’s diagnostic process. However, ICMs may present a significant amount of misqualified records due to artefacts and/or imperfections of diagnostic algorithms. P-wave oversensing (PWOS) is one of the plausible causes of inappropriate automatic analysis. In this report, a case of free-diver with recurrent syncope is investigated. The patient has undergone the implantation of Biomonitor 2-AF of Biotronik GmbH. Soon after implantation high ventricular rhythm (HVR) was registered. Manual analysis of the incident report revealed mild bradycardia and repetitive P-wave and periodic T-wave oversensing misqualified as HVR. Mechanism of PWOS and management options are discussed.