OBJECTIVE: The goal of the study was to evaluate differences in heart rate variability (HRV) among post-myocardial infarction (MI) patients, depending on their participation in the Croatian war and on established diagnoses of post-traumatic stress disorder (PTSD). METHODS: The study included 34 male war veterans with diagnosed PTSD who had suffered a first MI and 34 age-matched post-MI patients without PTSD. Cardiac autonomic balance was evaluated through HRV analysis. RESULTS: There were no differences in the mean R-R interval or overall HRV between the analyzed groups. Post-MI patients with PTSD had lower values for the square root of the mean of squared successive differences in R-R intervals (p = 0.02), the percentage of R-R intervals that were > or =50 milliseconds different from the previous interval (p = 0.03), and the high-frequency component (p = 0.03) but had higher values for the low-frequency component (p = 0.01) and the low-frequency/high-frequency ratio (p = 0.02), compared with post-MI patients without PTSD. CONCLUSION: Post-MI patients with PTSD have higher sympathetic and lower parasympathetic heart rate modulation activity, compared with patients with MI and no PTSD.