Introduction <p>Ultrasound use during cardiac arrest, particularly the Cardiac Arrest Sonographic Assessment (CASA) protocol, requires structured integration to identify reversible causes while minimizing interruptions in chest compressions. However, structured CASA training is not yet integrated into paramedic education in Thailand. The aim of this study was to evaluate the impact of a focused CASA mini-course on the knowledge and simulation-based diagnostic performance of Thai paramedic students.</p> Methods <p>This prospective pre-post study included third-year paramedic students. Participants completed a 90-minute CASA training course consisting of a 30-minute lecture and a 60-minute hands-on ultrasound session. Knowledge was assessed using a 10-item written test before and after the course. Diagnostic performance was evaluated through simulation-based assessments of CASA skills, including probe placement, image acquisition, and diagnostic interpretation. Participant satisfaction and confidence were also measured using a Likert scale.</p> Results <p>The mean post-test score significantly improved from 3.88 ± 1.36 to 8.81 ± 1.33 (<i>p</i> &lt; 0.001), with a large effect size (Cohen’s d = 2.68). Post-training diagnostic accuracy varied by condition. For core CASA components, accuracy was 75% for cardiac tamponade and 81.25% for sonographic features suggestive of pulmonary embolism. Ancillary EFAST interpretation accuracy was 62.5%. In simulation, 100% achieved correct probe placement, while 68.75% correctly diagnosed the reversible cause. Satisfaction scores were high, with an average confidence rating of 4.50 ± 0.63 and applicability to practice at 4.81 ± 0.40.</p> Conclusion <p>The structured CASA mini-course was associated with significant short-term improvements in knowledge and simulation-based diagnostic performance. These findings support the feasibility of integrating structured ultrasound training into paramedic curricula.</p>