In recent years evidence is increasing on the usefulness of physical loads and controlled physical training in patients with chronic heart failure (CHSS). In the presented work the authors assessed changes of the functional capacity and muscular strength after training on a bicycle ergometer. The group comprised 38 patients with CHSS due to IHD or dilatation cardiomyopathy NYHA II-III, EF lower than 40%, with a peak oxygen consumption (pVO2) lower than 20 ml/kg/min. The group was subdivided in a random fashion to subjects participating in training (T) and the control group (K). The patients were subjected to clinical examination, examination by common laboratory methods, spiroergometry, dynamometry. By the puncture technique a specimen of the m. vastus lateralis was taken for histological and histochemical examination of the muscle. The patients trained on the bicycle ergometer three times per week for a period of eight weeks, one exercise session lasted 30 minutes and was at the level of the anaerobic threshold. After completion of the training period the examinations were repeated. RESULTS Before the onset of training the groups did not differ in any indicators. After termination of training they increased in group T: pVO2 from 18.9 +/- 4.8 to 22.13 +/- 15.72 ml/kg/min. (p < 0.0004), the oxygen consumption at the level of the anaerobic threshold (VO2AT) from 13.4 +/- 3.4 to 15.96 < or = 3.75 ml/kg/min. (p < 0.0006), the respiratory quotient (RQ) from 0.93 +/- v0.09 to 0.97 +/- 0.006 (p < 0.05), the maximal tolerated load from 0.72 +/- 0.72 to 1.08 +/- 0.33 W/kg (p <0.002), the maximal voluntary contraction of the femoral quadriceps muscle (MVC START) from 291.2 +/- 70.1 to 328.1 +/- 66.0 N (p<0.01), the maximal voluntary contraction of this muscle after 20 mins. of repeated contractions (MVC END) from 157.6 +/- 109 to 290.1 +/- 64.9 N (p < 0.01), the decrease of the maximal contraction after 20 minutes of repeated contractions was from 52.8 +/- 32.1 to 12.4 +/- 5.0% (p < 0.01). After training there were statistically significant differences between groups in VO2AT (p < 0.01), in pVO2 (p < 0.03) and in the decrement of the maximal muscular contraction (p < 0.01). The authors found a trend towards normalization of the diameter of muscle fibres I and II and of their ratio. The ventilation equivalent for carbon dioxide VE/VCO2 during the maximal tolerated load correlated significantly with the systemic and pulmonary vascular resistance, with RQ, VO2AT, pVO2, with the maximal tolerated load and with the blood level of prostaglandin F. CONCLUSIONS Controlled physical training in patients with CHSS was safe, led to a significant improvement of spiroergometric indicators, load tolerance and muscular strength. After training there was a trend towards normalization of pathological changes in skeletal muscle. Based on the authors' experience and findings of other authors it is advisable to recommend training as part of treatment of patients with CHSS.