Treatment with FGF21 or JPH203 markedly increased levels of EF% (Fig. 5g and h) and FS% (Fig. 5g and i) and decreased levels of LVIDs (Fig. 5g and j),cardiomyocyte hypertrophy (Fig. 5g and k) and fibrosis (Fig. 5g and l) in T1D mice, suggesting that FGF21 can improve diabetes-associated cardiac structure damage and dysfunction. The gene discussed is FGF21; the disease is type 1 diabetes mellitus.