OBJECTIVE: Multicenter studies have shown that cardiovascular risks of ADHD medication are extremely low. However, QTc length has been shown to be increased in smaller samples of patients or case reports after stimulant and atomoxetine medication. Based on recent studies of genetic polymorphisms associated with drug-induced QTc prolongation and polymorphisms linkage to regional populations, we hypothesized that the drug-induced QTc prolongation could be a factor of particular polymorphisms linked to specific regional populations undistinguished in multicenter studies. METHODS: We included 69 patients from a region of central Slovakia, 36 patients were taking atomoxetine and 33 patients methylphenidate. QTc, heart rate, potassium levels and BMI were examined before and after 8 weeks of treatment. Therapeutic effect was measured by ADHD-RS-IV. RESULTS: We found QTc prolongation after 8 weeks of treatment both with atomoxetine and methylphenidate that was neither followed by the significant changes in BMI and potassium levels nor the significant increase of heart rate. CONCLUSION: This is the first study revealing QTc prolongation in the group of ADHD children from the same region after 8-week treatment with atomoxetine and methylphenidate, indicating the potential discrete abnormalities in cardiac functioning associated with polymorphisms in genes of dopaminergic and noradrenergic system.