Studies reveal that the gut microbiota and its metabolites play an important role in the pathogenesis and progression of various cardiovascular diseases，and are inseparably related to the prognosis of the disease.In patients with heart failure，splanchnic hypoperfusion leads to intestinal ischemia and alters intestinal permeability，and then translocates bacteria and their toxins into the blood circulation，triggering local orsystemic inflammatory responses. Trimethylamine N - oxide(TMAO)，as a metabolite of gut microbiota，is involved in the pathological process of heart failure，such as exacerbating cardiac hypertrophy and fibrosis，inducing inflammatory responses，and worsening heart failure by affecting renal function. This article reviews trimethylamine N-oxideas as the therapeutic target of heart failure and as a prognostic marker of heart failure.