In this paper we have compiled and summarized the steps which manufacturers and clinical investigators need to undertake to perform a target population definition during the Health technology assessment process of medical device, namely external cardio stimulator (pacemaker). Based on available data using top-down approach we have defined target population for external cardiostimulator and estimated, that the size of the target population for external pacing will not exceed 16000 patients per year in the Czech Republic and is of comparable size with other states in the region.