Heart Failure Inclusion Criteria:  Age ≥18; A clear diagnosis of coronary heart disease; NYHA cardiac function grade ≥III and/or LVEF≤40%; Voluntarily signed the informed consent.  Control Inclusion Criteria:  The spouse of the case group; Age ≥18; No previous clear diagnosis of coronary heart disease; The LVEF: 50 ~ 80%; Voluntarily signed the informed consent.  Exclusion Criteria:  Have received major gastrointestinal surgery (including gallbladder and appendectomy) within 5 years; Inflammatory bowel disease (IBD), including ulcerative colitis, Crohn's disease, or colitis; Acute gastroenteritis; Clostridium difficile (recurrent) or Helicobacter pylori infection; Persistent or chronic diarrhea; Chronic constipation; Peptic ulcer; Polyps in the stomach or intestines; Gastrointestinal neoplasms; Irritable bowel syndrome; Acute or chronic cholecystitis, hepatitis; Take or inject antibiotics and probiotics in the past 3 months End-stage disease (life expectancy less than 3 months); Pregnant or pregnant during follow-up; Failure to give informed consent (e.g. severe cognitive impairment); The patient has been enrolled in other ongoing clinical trials.