Introduction: Coronary Artery Disease (CAD) remains the leading cause of death in Brazil, with literature indicating that in patients post-acute myocardial infarction, reduced Heart Rate Variability (HRV) has been established as a risk factor. One of the studied practices to aid in rehabilitation is meditation, believed to alter physiological aspects related to stress such as respiratory rate, oxygen consumption, carbon dioxide production, and systolic blood pressure, suggesting a better sympathetic-vagal balance.

Objective: To assess the effects of Zazen meditation practice on heart rate variability in patients with recent acute and chronic myocardial infarction. Methodology: Randomized Clinical Trial. Chronic assessments will include: HRV with Polar H10 heart rate monitor, Quality of Life assessment with SF36 Quality of Life and Health questionnaire, Spiritual assessment with WHOQOL SR Spirituality, Religiosity, and Personal Beliefs questionnaire, Biochemical Parameters with ultra-sensitive PCR and cortisol, Ventricular Ejection Fraction (VEF), and 6-minute Walk Test (6MWT). Acute assessments will include: HRV with Polar H10 heart rate monitor, before and after a meditation session, in time and frequency domains. Sample size calculation was performed using Winpepi software version 11.43, with a power of 80% and significance level of 5%, determining a sample of 44 individuals. For intra-group differences analysis, ANOVA for repeated measures and/or its non-parametric counterpart, Friedman Test, will be used. For proportion analysis and comparison, Chi-square Test will be used. Expected

Results: It is expected that the findings will contribute to a better understanding of the potential benefits that a meditation intervention may bring to patients who have experienced acute myocardial infarction.