The results of HRV analysis in patients with hypertrophic cardiomyopathy (HCM) are conflicting. We evaluated short-term HRV in patients with familiar HRV and in their close relatives. 31 families of patients with HCM were examined. There were 43 patients with HCM confirmed by 2D-echo (HCM-group, 23 f, 20 m, aged 46 +/- 14 ys), and 157 family members (REL-group, 75 f, 82 m, aged 29 +/- 17 ys). The control group consisted of 180 healthy subjects (80 f, 100 m, aged 33 +/- 12 ys). In each subject 512 consecutive sinus beats were recorded in supine position during spontaneous breathing using computer-assisted amplifier (A/D 12 bit, 1 kHz). Mean RR interval (RRI, ms), its standard deviation (SDRR, ms) and spectral measures (FFT, Blackman-Harris window): PSD of high frequency (HF) and low frequency (LF) [ms2/Hz], as well as respiratory rate (BPM) were measured. Patients with HCM had significantly shorter RRI (867 +/- 121) as compared to the controls (919 +/- 138, p < 0.05). The RRI was also shorter in the relatives (851 +/- 150, p < 0.01). In HCM and REL groups the respiratory rate was faster (16.7 +/- 3.0 and 17.1 +/- 3.4, respectively), as compared to the controls (14.5 +/- 2.9, both p < 0.01). The HRV measures were reduced in the HCM-group (SDRR 31.4 +/- 10.6, lnHF 7.71 +/- 0.65, lnLF 8.22 +/- 0.65 and LF/HF 1.07 +/- 0.10), as compared to the controls (SDRR 64.8 +/- 23.9, lnHF 8.79 +/- 0.61, lnLF 8.87 +/- 0.65, all p < 0.001 and LF/HF 1.01 +/- 0.07, p < 0.01). In the REL-group SDRR and lnHF were significantly reduced (SDRR 52.4 +/- 24.1, lnHF 8.48 +/- 0.78, p < 0.001), while the remaining parameters were comparable. The HRV reduction was more expressed in HCM-patients and family-members < 30 years of age. A significantly reduced age-, sex- and RRI-adjusted SDNN was observed in 54% pts in HCM-group and in 42% subjects in members-group. Reduced heart rate variability is frequently seen not only in patients with diagnosed HCM, but also in a substantial number of their kindred.