Introduction: Sick Euthyroid syndrome is linked with alteration in thyroid function. It is seen in many non-thyroidal illnesses. But its major implications are seen in Acute Myocardial Infarction. Abnormalities of thyroid function tests are seen in this condition. These abnormalities include a decrease in free T3 or both a decrease in FT3 and a decrease in free T4. This has shown to be as a marked prognostic indicator in this Acute Myocardial Infarction. Sick Euthyroid syndrome is contemplated to be ‘benign’. It has been shown for increased morbidity and mortality. This is the reason why this is considered as prognostic marker. Hence the study was conducted to assess the thyroid function in Acute Myocardial Infarction and its further link with immediate out come of patients with Acute Myocardial Infarction. Methods: 50 Consecutive patients of Acute Myocardial Infarction admitted in our institute was our study group. A thorough history, complete clinical work-up, detailed systemic work-up was done. Further investigations such as 2 D Echo to assess left ventricular function, multiple electrocardiograms and Creatinine phosphokinase-MB levels were done. In addition to this from total T3, T4 and TSH were done. These were taken 24-36 hours after onset of chest pain on day. Reports were taken again on day 7. Results: The mean age for males was 58±12 years and 61±9 years in females. The male: female ratio was 2.1:1. There was no significant difference in the mean values of T3, T4 and TSH on days 1 and 7. Statistically significant association which is p<0.05 was observed between the day 1 serum T3 and CK-MB, cardiogenic shock, acute complications and decreased Left ventricular ejection fraction. Conclusion: Abnormal thyroid function in Acute Myocardial Infarction is a poor prognostic indicator. It indicates poorer cardiac function in form of decreased left ventricular ejection fraction. Thus this leads to increased mortality. The sick-euthyroid syndrome is characterized as a decreased free T3 levels that occur in a setting of non-thyroidal illness without any thyroid or hypothalamic-pituitary dysfunction. It most frequently is seen in patients with MI, and is associated with a higher mortality.