The aim of this study was to assess the influence of amiodarone hydrochloride on time- and frequency-domain parameters of signal-averaged electrocardiogram (SAECG) in patients with ischaemic heart disease (IHD). The study population consisted of 33 patients (18 female and 15 male), mean age 59.2 +/- 7.7. Amiodarone hydrochloride was orally used in the initial dose 600 mg/day for 10 days, and subsequently 200 mg/days for 6 weeks. Recording of SAECG and ambulatory Holter monitoring were made at baseline and in 10 day and after 6 weeks of therapy. The following time-domain parameters were analyzed: the root mean square voltage of the last 40 and 50 ms of the filtered QRS (RMS40 i RMS50), total time duration of filtered QRS (t-QRS) and duration of low amplitude signals < 40 microV in the terminal part of QRS (LPD). Late potentials (LP) were recognized when at least two from three criteria were fulfilled: 1) RMS40 < 20 microV, 2) t-QRS > 114 ms, 3) LPD > 38 ms. Frequency analysis of SAECG allowed to calculate the following parameters in logarithmic scale: energy spectrum > -60 dB (A) and decibel drop at 40Hz (Dd) and also in linear scale: area ratio 20-50/0-20Hz (Ar) and magnitude ratio (MR1-7). The values of RMS40 and RMS50 did not significantly change during amiodarone therapy. The obtained values of t-QRS were significantly longer after antiarrhythmic therapy, respectively 97.8 +/- 9.1 ms at the baseline, 102.1 +/- 10 ms after 10 days (p < 0.05), and 104.1 +/- 10.4 ms after 6 weeks (p < 0.005). Moreover the values of LPD did not significantly change after amiodarone treatment. At the baseline the presence of LP were observed in 3 (9%), after 10 days were recorded in 8 (24%), and after 6 weeks in 7 (22%) cases. Only in one case the LP were observed during the whole antiarrhythmic therapy. Moreover, amiodarone hydrochloride did not statistically significant change frequency-domain parameters in logarithmic scale and in linear scale.