Medical personnel carrying out electrical cardioversion (EC) procedures must remember to have the R-wave sync mode switched on, use the correct energy and maintain personal safety. The defibrillators used by medical response teams most often switch out of cardioversion mode once a shock is delivered. Therefore, this mode must be switched on again before subsequent shocks are delivered. The main aim of the study was to assess the ability of emergency medical teams participating in emergency medicine championships to perform EC. The research was a retrospective observational study and was based on an analysis of the evaluation sheets from two tasks simulating the management of a patient with unstable tachycardia conducted during the International Winter Emergency Medicine Championships. Three-person teams consisting of paramedics and representing the Polish emergency services were included in the study. The team representing the championship organiser and the few foreign teams participating in the competition were excluded from the study. The decision to conduct EC was taken by 36 teams (83.72%) in 2015 and 27 teams (87.10%) in 2019. In both editions of the championships, during consecutive shocks, the percentage of actions performed correctly decreased significantly-switching on synchronisation mode in 2015 (94.4%, 83.33%, 72.22%) and in 2019 (100%, 88.89%, 81.48%); correct energies in 2015 (91.67%, 80.56%, 77.78%) and in 2019 (92.59%, 85.19%, 81.48%); shocks in a safe manner in 2015 (94.44%, 94.44%, 91.67%) and in 2019 (100%, 96.30%, 96.30%). Teams participating in the assessed tasks in a significant majority of cases correctly qualified the patient for EC, and correctly carried out the actions required for this procedure. It is of particular note that with every subsequent shock, the percentage of shocks carried out without the sync mode increased significantly.