The goal of this study was to compare various methods of anaerobic threshold (AT) determination and to estimate its importance for both the prescription of appropriate physical activity and long‐term follow‐up evaluation in patients with chronic heart failure (CHF). Twenty‐eight persons (New York Heart Association Classification II, III) passed a symptom‐limited spiroergometrical test; some of them were serially measured. The incremental work rate was graded by 0.25 W‐kg‐1every 4 minutes. AT was determined from ventilatory parameters (VT), on the one hand, and from base excess changes (—BET), on the other. VT was determined in 79% and—BET in 50% of patients. The correlation between other functional parameters and both VT and‐BET parameters was close (r = 0.94 for heart rate, for example). The possibility of making an AT determination decreased in Weber's class C patients. AT determination was also possible in persons showing a change in acid‐base balance at rest. Basic functional parameters (heart rate, oxygen uptake) and rating of perceived exertion determined at AT showed a high interindividual variability. The mean value corresponded to 60% of maximum level of exercise tolerance. It was concluded that AT could be determined in a high percentage of persons with CHF even if determination of a clear result decreased with increasing severity of illness. VT could be determined more frequently than‐BET; nevertheless, the results obtained by these two methods were comparable. The AT level was determined to be an objective criterion for definition of illness severity and its progress. AT may be used not only for long‐term evaluation of therapy effectiveness, but also for the prescription of a safe limit for physical activity.