Metoprolol is contraindicated in acute heart failure, mainly to avoid causing bradycardia or cardiac arrest, resulting in patient death. 1. Acute heart failure patients, mainly due to a sharp decline in myocardial function, resulting in cardiac contraction weakness, systemic blood supply, water retention, and then appear dyspnea, pulmonary edema and other critical manifestations, clinical treatment to enhance myocardial strength, reduce myocardial burden, commonly used drugs are diazepam, furosemide, etc.. 2. Metoprolol is a β-receptor antagonist, the main mechanism of action is to inhibit the function of β-receptors, thereby reducing the heart rate, reducing myocardial oxygen consumption, thereby reducing the burden on the myocardium, but can not be applied to patients with a heart rate of less than 60 beats per minute, which may lead to cardiac arrest. 3. Acute heart failure is usually accompanied by slow heartbeat and intermittent cardiac arrest, if taking metoprolol, it may lead to a further decline in heartbeat, systemic ischemia, hypoxia, and in severe cases, it may lead to cardiac arrest, resulting in the death of the patient, so metoprolol is usually prohibited in acute heart failure. Acute heart failure is a serious condition, it is recommended to seek timely medical treatment, under the guidance of the doctor for active and effective treatment to improve the survival rate of patients.