Objective: To investigate the changes of cardiac function in non-ST-segment elevation acute myocardial infarction patients with low T3 syndrome.Methods: 212 cases of patients with non-ST-segment elevation acute myocardial infarction were enrolled in this study. NT-proBNP, cTnI, renal function and thyroid function were examined at the time of admission. Cardiac function Killip classification was made according to the lung rales and the risk stratification was made based on clinical features. The ejection fraction was measured by echocardiography within 24 hours of admission. According to the thyroid function test, the patients were divided into low T3 group and normal T3 group. NT-proBNP levels, troponin levels, left ventricular ejection fraction, Killip classification frequency distribution, and frequency distribution of risk stratification were compared between the two groups.Results: There were 126 cases in normal T3 group and 86 cases in low T3 group. Compared with normal T3 group, NT-proBNP level in low T3 group was significantly higher (P=0.002), the proportion of patients with heart function Killip grade III + IV significantly increased (P=0.008), the left ventricular ejection fraction decreased (P=0.035), the proportion of high-risk patients and high-risk patients based on GRAC scores increased significantly (P=0.006), and severe cardiovascular events (ventricular tachycardia, ventricular fibrillation, cardiogenic shock, sudden death, etc.) increased (P=0.075).Conclusion: Non-ST-elevation acute myocardial infarction with low T3 syndrome has poor heart function and serious condition.