In UK cardiac rehabilitation programmes, exercise training is often set at a percentage of maximal heart rate or heart rate reserve, either predicted or measured. Problems may arise when using this method for chronic heart failure (CHF) patients who often have chronotropic incompetence and are treated with beta blockers. A safer approach is to use cardiopulmonary exercise testing to prescribe training below the ventilatory threshold, thus ensuring that the exercise is moderate. The aim of this study was to determine whether British Association for Cardiac Rehabilitation (BACR) heart rate guidelines prescribe moderate intensity exercise for CHF patients. The only target heart rate range to prescribe exercise below the ventilatory threshold was 60–80% measured maximum heart rate. Target heart rates calculated from predicted maximum values were higher than those from measured values, and the heart rate reserve method resulted in the highest target heart rates. Cardiac rehabilitation exercise practitioners should be aware that these methods may well result in CHF patients performing heavy rather than moderate exercise.