Cardiomyoplasty is a procedure developed to improve heart performance in patients suffering from congestive heart failure. The latissimus dorsi muscle (LD) is surgically wrapped around the failing ventricles and stimulated to contract in synchrony with the heart. The LD is easily fatigued and as a result is unsuitable for cardiomyoplasty. For useful operation as a cardiac assist device, the fatigue resistance of the LD must be improved, whilst retaining a high power output. The LD of rabbits was subjected to a training regime in which cyclical work was performed. Training transformed the fibre type composition from approximately equal proportions of fast-oxidative-glycolytic (FOG) and fast-glycolytic (FG) fibres to one composed of almost entirely of FOG with no FG, which increased fatigue resistance whilst retaining rapid contraction kinetics. Muscle mass and cross-sectional area increased but power output decreased, relative to control muscles. This training regime represents a significant improvement in terms of preserving muscle mass and power compared with other training regimes, whilst enhancing fatigue resistance, although some fibre damage occurred. The power output of the trained LD was calculated to be sufficient to deliver a significant level of assistance to a failing heart during cardiomyoplasty.