36 Medical students are allocated randomly to Peers' group where they are trained on BLS skills by senior students.

Four students from the latest three years of study in medical schools in Syria (4th, 5th, and 6th) are randomly selected and enrolled to be instructors for basic life support training course to transfer the resuscitation skills to medical students from pre-clinical years.

36 students are allocated randomly to professionals' group where they are trained on BLS skills by professional trainers in emergency. Four professionals (2 emergency doctors, cardiologist and anesthesiologist) are leading training to the control group to deliver the basic life support training course with the same duration and content as the intervention group.

A course design was made to be consistent with ERC guidelines with local modifications made by emergency professionals in duration, instructor-to-trainee ratio, course materials, methods to deliver these materials theoretically, and the type of the manikin used to practice CPR. One-day-course consisting of 75, 20, 20, 20 minutes for theoretical BLS, chocking, recovery position, the practical representation of BLS scenario respectively followed by 40-minute practical training on BLS skills for each subgroup. Both arms of the study follow the same timeline and no extra time is given to any group.

Same manikins were used for the training and the assessment. On the day of the experiment students in each arm are divided into 4 subgroups of maximum 9 students, each led by two trainers of BLS skills with a maximum ratio of 2 instructors to 9 students per group.

A practical simulated scenario assessment using a checklist based evaluation in objective structured clinical examination (OSCE) design. The checklist is constructed in accordance to European resuscitation council (ERC) guideline. Students should perform each point correctly to pass the assessment (1- Safe approach, 2- call for help, 3- opening airway, 4-checking cardiopulmonary situation, 5- call ambulance, 6- CPR with effective depth, 7-rate and 8-position, 9-rescue breaths).

a 20-item questionnaire with 3 checkpoints per item (60-point-scale) derived from ERC materials after testing the applicability of the questionnaire by a pilot study.