The immediate effects on cardiac function of 3-weekly docetaxel and combined docetaxel-epirubicin were evaluated during treatment of metastatic breast cancer using assessment of heart rate variability (HVR) and left ventricular ejection fraction (LVEF) measured by echocardiography. Twenty-four breast cancer patients were treated with docetaxel alone (starting dose 100 mg/m2) and 34 with a combination of docetaxel and epirubicin (starting dose for both drugs 75 mg/m2) administered 3-weekly. Single docetaxel caused no significant changes in HVR or cardiac function, whereas during combined treatment statistically significant changes were observed in mean RR intervals and in the number of supraventricular extrasystoles. Clinically the observed changes were insignificant. In conclusion, in 3-weekly administration the combined use of docetaxel and epirubicin was more likely than single docetaxel to cause changes in cardiac function.