BACKGROUND: The aim of the study was to appraise time domain heart rate variability (HRV) parameters in patients with ST-segment elevation myocardial infarction (STEMI) in different age groups. MATERIAL AND METHODS: Retrospective analysis included 357 consecutive patients in sinus rhythm without diabetes, aged 27-87 years (mean age--63.0 +/- 11.8 years, 243 men) treated with primary percutaneous transluminal coronary angioplasty (PTCA) due to first in their life STEMI. Each patient had an echocardiographic examination and 24-hour ECG monitoring results interpreted. Participants were divided in the analysis applying the WHO old age criterion into two groups: group A < 65 years old (n = 188) and B aged > or = 65 years (n = 169). RESULTS: In the whole study group age negatively correlated with SDNN, SDANNI, SDNNI and EF, whereas positive correlation between EF and SDANN, and EF and SDNNI was observed. Elderly patients as compared to the younger individuals had significantly diminished SDNN, SDANN, SDNNI and more often SDNN < 70 ms (33.7% vs 20.7%, p < 0.0001). When the circumflex artery lesion was the cause of myocardial infarction SDNN and SDANN were significantly lower in the group B, whereas in case of PTCA of RCA, apart from decreased SDNN and SDANN, EF was also compromised in this group. CONCLUSIONS: Elderly patients with myocardial infarction with ST-segment elevation treated with primary PTCA, compared to the younger age group, are characterized by increased sympathetic activation assessed by heart rate variability and heart rate in 24-hour ECG monitoring.