College students report stress and anxiety when taking science courses, such as anatomy & physiology. Mindful breathing is a technique that can be used in the classroom before taking exams. To determine the impact of mindful breathing exercises on the student experience, students were randomly assigned to either course sections that included mindfulness breathing or those that did not. Both groups completed the modified twenty-question Anxiety State Self-Evaluation Questionnaire before each exam. Students in the intervention group were asked to participate in a 5-minute guided breathing exercise after completing the questionnaire, but before taking each exam. One hundred and six students (86.2%) took all four exams in the intervention group and 101 students (91.8%) in the control group. Students in the intervention group reported higher mean scores for almost all positive emotions before all four exams. The mean scores for statements describing negative emotions were generally higher for the control group than the intervention group. The guided mindful breathing intervention had no positive impact on exam performance in this study. However, the results of our study using guided mindful breathing exercises prior to taking an exam demonstrated that there was a beneficial effect on students' emotional state. Future research should explore other strategies designed to decrease test-related stress and anxiety to evaluate any potential influence on academic performance.