BACKGROUND: Enhanced sympathetic activity is a potential cause of increased risk of cardiovascular complications during treatment of hypertension and type 2 diabetes. MATERIAL AND METHODS: Heart rate variability (HRV) was assessed before and after 12-16 weeks of treatment with calcium antagonists in 89 patients with mild and moderate hypertension. RESULTS: Changes of majority of parameters of 24 hour blood pressure monitoring were in general favorable however lowering of magnitude and rate of morning blood pressure rise was observed only in verapamil treated patients. Analysis of HRV showed that treatment with all long acting calcium antagonists under study was associated with enhancement of sympathetic activity. In supine position nifedipine treated compared with verapamil treated patients exhibited greater sympathetic activity. In upright position changes of HRV parameters characteristic for increased sympathetic activity were also more pronounced in dihydropyridine treated compared with verapamil treated patients. CONCLUSION: Effect of calcium antagonists on parameters of HRV is negative and this should be taken into consideration when antihypertensive treatment of patients with hypertension and type 2 diabetes is selected.