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Endurance exercise promotes adaptive growth and improved function of myocytes, which is supported by increased mitochondrial activity. In skeletal muscle, these benefits are in part transcriptionally coordinated by peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α). The importance of PGC-1α to exercise-induced adaptations in the heart has been unclear. Here we show that deleting PGC-1α specifically in cardiomyocytes prevents the expected benefits from exercise training and instead leads to heart failure after just 6 weeks of training. Consistent with this, in humans, rare genetic variants in PPARGC1A, which encodes PGC-1α, are associated with increased risk of heart failure. In this model, we identify growth differentiation factor 15 (GDF15) as a key heart-secreted mediator that contributes to this dysfunction. Blocking cardiac Gdf15 expression improves cardiac performance and exercise capacity in these mice. Finally, in human heart tissue, lower cardiomyocyte PPARGC1A expression is associated with higher GDF15 expression and reduced cardiomyocyte density. These findings uncover a crucial role for cardiomyocyte PGC-1α in enabling healthy cardiac adaptation to exercise in part through suppression of GDF15.