Health professionals often witness in-hospital episodes of cardiac arrest. The quality of the Cardiopulmonary Resuscitation (CPR) depends on the level of theoretical background and practical skills. Purpose: The aim of the present study was to investigate the level of theoretical knowledge of skilled cardiologists and anesthesiologists in the Basic and Advanced Life Support (BLS/ ALS). Material - method: In this study, sample included 240 cardiologists and anesthesiologists, chosen randomly from employers of 17 General Public Hospitals of Athens. For data collection, a questionnaire with 16 theoretical questions was designed, based on the guidelines of the European Resuscitation Council (ERC) 2005. Significance level was set at p=≤0,05. The analysis was performed with the Statistical Package IBM SPSS Statistics 19. Results: No statistically significant difference was observed between specialists cardiologists and anesthesiologists in overall performance in theoretical knowledge on the BLS and ALS. Additionally, no statistical significance was observed between the two separate groups of theoretical background. Statistically significant difference was observed among those who had participated in a training seminar in BLS and ALS and those who had not participated (p<0,001). Also, there was statistical significance between the follow-up seminar in BLS/ ALS and specialty for the right answer to the question "which is the right ratio of chest compressions and ventilation", (p<0,001). Conclusions: The level of background knowledge of specialist cardiologists and anesthesiologists in the algorithms of BLS and ALS seem to correlate to the attendance of a training course.