Introduction: Due to the complexity of the situation and rapid changes in patients' clinical status in intensive care units, it is necessary to teach decision-making skills to nurses, alongside critical thinking. The aim of this study was to evaluate critical thinking training by using critical thinking cards on clinical decision-making of nurses in cardiac care units (CCU). Methods: In this quasi-experimental study, 74 CCU nurses from the selected hospitals affiliated to Ahvaz and Dezful Universities of Medical Sciences were selected based on the inclusion criteria and were assigned to either the intervention or the control group by using permuted block randomization. The data were entered into SPSS V22 and analyzed. Results: There was no statistically significant difference between the demographic characteristics of the two groups ( P < 0.05). The mean total score of nurses' clinical decision-making before training sessions in the intervention group was calculated to be 141.59 ± 10.76, which was lower compared to a score of 148.56 ± 10.95 in the control group ( P = 0.011). Therefore, covariance analysis was used to modify the results. The mean total score of nurses' clinical decision-making after the training in the intervention group was calculated as 163.82 ± 8.83, indicating a significant increase compared to a score of 154.50 ± 11.25 in the control group ( P < 0.001). Conclusion: The findings of the present study show that the education of critical thinking by using the critical card tool leads to improved clinical decision-making in CCU nurses.