BACKGROUND: Imbalance in autonomic nervous system and impaired myocardial repolarization have been shown to increase the risk for arrhythmias in patients with arterial hypertension. This study evaluated the effects of masked hypertension on QT interval dynamicity. METHODS: The study group consisted of 108 consecutive patients with masked hypertension and 102 control subjects. Twenty-four-hour Holter monitoring was performed before anti-hypertensive treatment. CONTEC holter software was used to calculate HRV and QT dynamicity parameters. All subjects had a complete history, laboratory examination, and transthoracic echocardiography. RESULTS: There was no significant difference in age-gender distribution between patients and controls. Non-sustained VT was present in four patients (2.9%). SDNN, RMSSD, PNN50, LFnu, HFnu were significantly decreased in masked hypertension, whereas LF/HF ratio was significantly increased. QT/RR slopes over 24 hours were significantly increased in masked hypertension for QT end and QT apex (QTapex/RR: 0,15 +/- 0,12 vs 0,27 +/- 0,18 p < .001; QTend/RR: 0.19 +/- 0.12 vs 0.35 +/- 0.22, p < .001). CONCLUSIONS: This study showed for the first time that masked hypertension was associated with a significant worsening of HRV and QT dynamicity parameters.