To explore frontline decision-making, adaptation, and learning in ambulance care during the evolving COVID-19 pandemic. Descriptive and interpretative qualitative study. Twenty-eight registered nurses from the Swedish ambulance services described 56 critical incidents during the COVID-19 pandemic through free-text questionnaires. The material was analysed using the Critical Incident Technique and Interpretive Description through the lens of potential for resilient performance. The findings were synthesized into four themes: 'Navigating uncharted waters under never-ending pressure', 'Balancing on the brink of an abyss', 'Sacrificing the few to save the many' and 'Bracing for the next wave'. Frontline decision-making during a pandemic contribute to ethical dilemmas while necessitating difficult prioritizations to adapt and respond to limited resources. Learning was manifested through effective information sharing and the identification of successful adaptations as compared to maladaptations. During pandemics or under other extreme conditions, decisions must be made promptly, even amidst emerging chaos, potentially necessitating the use of untested methods and ad-hoc solutions due to initial lack of knowledge and guidelines. Within ambulance care, dynamic leadership becomes imperative, combining autonomous frontline decision-making with support from management. Strengthening ethical competence and fostering ethical discourse may enhance confidence in decision-making, particularly under ethically challenging circumstances. Performance under extreme conditions can elevate the risk of suboptimal decision-making and adverse outcomes, with older adults being especially vulnerable. Thus, requiring targeted decision support and interventions. Enhancing patient safety in ambulance care during such conditions demands active participation and governance from management, along with decision support and guidelines. Vertical communication and collaboration between management and frontline professionals are essential to ensure that critical information, guidelines, and resources are effectively disseminated and implemented. Further research is needed into management and leadership in ambulance care, alongside the ethical challenges in frontline decision-making under extreme conditions. Findings are reported per consolidated criteria for reporting qualitative research (COREQ). No Patient or Public Contribution.