Assessment and prediction of the functional state of specialists in an extreme professional environment is a physiological justification for the organization of labor to maintain the high performance of specialists. The purpose of the work is psycho diagnostic and electrophysiological study of the functional state of firefighter-rescuers with different service lives in the Federal Firefighting Service of the Ministry of Emergencies in the Tver region, taking into account the daily dynamics. Materials and methods: the survey involved 235 male rescue firefighters aged 25 to 45 years with a service experience from 1 to 22 years. All subjects were divided into three groups depending on the length of service. To assess the functional state, we used a questionnaire with scales of well-being, activity and mood, and a method of heart rate variability. Results: the subjective assessment on the scale of the questionnaire was optimistic, homogeneous and quite rigid. Analysis of heart rate variability showed a more heterogeneous picture. When assessing the daily dynamics, a vagotonic shift was detected in most firefighter-rescuers. Correlation analysis revealed balanced adequate connections between the self-assessment of the functional state and the hardware diagnosis of heart rate variability only for firefighter-rescuers with 7–15 years of service experience, which corresponds to the stage of formed professionalism.