Thyroid Hormone Replacement for Hypothyroidism and Acute Myocardial Infarction(ThyroHeart-AMI)

Inclusion Criteria: 1. Age 18 - 75, male or non-pregnant female; 2. Is diagnosed acute myocardial infarction and received primary percutaneous coronary intervention (PCI); 3. With presence of hypothyroid status (i.e., TSH \>7.0 mIU/L and (or) fT3 \<1.79 pg/mL); 4. Is able to understand the objective of the trial, takes part voluntarily and signs the written informed consent form. Exclusion Criteria: 1. Those who have participated in other drug or therapeutic equipment clinical trials but do not reach the main study endpoint time limit; 2. Symptoms of severe heart failure (Killip Class III and above); 3. Severely impaired renal function before surgery: serum creatinine \> 2.0mg/dl; 4. Impaired liver function before surgery: Serum GPT \> 120U/L; 5. Those who have prior thyroid diseases and already on levothyroxine or anti-thyroid medicines; 6. Those taking medicine which can affect the test of thyroid function; 7. Patients who plan to undergo coronary artery bypass grafting or other surgery within 3 months; 8. Those having prior myocardial infarction; 9. Patients who are deemed by the researchers to have low compliance and unable to abide by the requirements and complete the study.