The effects of docetaxel treatment on autonomic cardiac function was studied with 24-h ECG recordings in breast cancer patients pretreated with anthracyclines. Twenty-four women were evaluated before docetaxel treatment and after 3-4 courses of docetaxel 100 mg/m(2). The heart rate, cardiac extrasystoles and heart rate variability (HRV) in both the time and frequency domain were assessed from 24-h ECG recordings. The acute effects of docetaxel were calculated from 1-h recordings immediately prior to, during and after infusion. Long-term effects were evaluated from 24-h recordings performed before treatment and after 3-4 courses of docetaxel. There was no increase in the number of cardiac extrasystoles during docetaxel infusion. The number of ventricular extrasystoles decreased from 14 (23) to 7 (14) during and 5 (10) after the first infusion (p=0.02). The heart rate, HRV and extrasystoles were similar before and after 3-4 courses of docetaxel. The treatment did not abolish circadian variability of the heart rate. Docetaxel did not deteriorate autonomic cardiac function. In conclusion, our findings suggest that docetaxel does not have harmful cumulative effects on autonomic control of the heart and is therefore unlikely to be cardiotoxic.