Unstable angina pectoris is accompanied by several unfavourable autonomic disturbances. A noninvasive assessment of the autonomic cardiac control is possible by means of heart rate variability analysis (HRV). 26 patients with unstable angina pectoris were enrolled in the study. All patients received obligatory nitroglycerin and heparin intravenously within two days, and gallopamil (G) or metoprolol (M) together with aspirin or ticlopidine orally randomly, which were continued for 3 month or shorter if coronary revascularization was earlier performed. 512 R-R intervals was registered in each patient at 7th day of hospitalization and in 14th at the time of admission. Kardioassist v.1.0 system was used for heart rate variability analysis. After analog to digital conversion, with 12 bit resolution and 1000 Hz of sampling rate, seriogram of R-R intervals was obtained, and then power spectrum density was computed with the Fast Fourier Transform. Time-domain analysis provided mean (basic) R-R interval (BCL) and its standard deviation (SD-RR). In frequency-domain the following spectral variables were analysed: power spectral density (s2/Hz) of the high frequency component (aHF, 0.15-035 Hz), low frequency component (aLF, 0.05-0.15 Hz) and very low frequency component (aVLF, 0.004-0.05 Hz), percentage power of respective components (%HF, %LF and %VLF) and autonomic balance indices: aLF:aHF and %LF:%HF. These variables were compared in patients treated with G (13 patients) against those with M (13 patients). Additionally, the effects of treatment regimen was evaluated also in 14 patients, in whom HRV analysis was performed at admission and 7 days later.(ABSTRACT TRUNCATED AT 250 WORDS)