Introduction: First aid is a set of procedures aimed at the immediate treatment of patients with acute illnesses or injuries, with the main goal of saving lives and preventing potentially dangerous situations. In addition to properly performed chest compressions and adequate ventilation, it is crucial to perform timely defibrillation of shockable rhythms according to valid ERC guidelines. Aim : To examine and compare the level of knowledge of Nursing students of the Faculty of Health Studies of the University of Rijeka and 5th grade students of the Secondary School of Medicine in Rijeka about providing first aid and the automatic external defibrillator, as well as to compare the knowledge depending on whether the student/student has undergone some form of education about providing first aid and using AED or not. Participants and methods: The research was conducted through a questionnaire on a convenient sample of N= 121. The research included students of the Faculty of Health Studies in Rijeka, N=71 and students of the Secondary Medical School in Rijeka, N=50. An online questionnaire consisting of four questions was used: sociodemographic data, a 10-question multiple-choice knowledge test, questions about AED, and an attitude scale about first aid, resuscitation, and AED. Results: The results of the study indicate significant differences in knowledge and attitudes on the provision of first aid and applying an automatic external defibrillator according to the demographic characteristics of the respondents. Professional studies, especially those of the male sex, the older respondents and the students of the higher years of study showed better knowledge and more positive attitudes according to the first aid and use of AED. Conclusion: These studies point to the importance of continuous education and repetition of training on providing first aid and using AED in order to maintain a high level of competence. Furthermore, the existence of formal training programs on CPR in schools can be of crucial importance for increasing citizens' awareness and readiness for timely response in case of medical emergencies. Ultimately, improving knowledge and skills in providing first aid and using AED can significantly contribute to increasing survival rates in the event of cardiac arrest and other medical emergencies.