Approximately 60 patients with ST-segment elevation myocardial infarction successfully treated with primary percutaneous coronary intervention will be enrolled and randomized to receive the sodium tanshinone IIA sulfonate in addition to standard therapy or the same volume/day of normal saline.

The primary endpoint is the variation in LV end-diastolic volume index (LVEDVi) assessed with cardiac magnetic resonance imaging (MRI) at baseline and 6 months.

The primary endpoint is to determine whether sodium tanshinone IIA sulfonate could prevent LV remodeling among patients with completely reperfused AMI after PCI, detected by 6 month change in LVEDVi measured using cardiac MRI when compared to placebo.

Secondary endpoints will include cardiac MRI measures of variations in microvascular obstruction, defect size, ventricular wall motion score, wall thickening, global LV ejection fraction, ventricular volumes (LV end-systolic/ diastolic volume) and myocardial perfusion during the same interval.

Furthermore, the investigators will determine the variation (change from baseline) of biomarkers indicating myocardial fibrosis (PICP, PIIINP, ICTP and MMPs) and NT-ProBNP at 1 and 6 months after AMI.

Additional efficacy endpoints will include 6-minute walk test, New York Heart Association functional classification, Seattle Angina Questionnaire score and incidence of cardiovascular events (defined as cardiogenic death, stroke, recurrent myocardial infarction, readmission on account of deterioration of congestive heart failure or unstable angina, target vessel revascularization) at the 6-month follow-up will also be analyzed to evaluate the efficacy of sodium tanshinone IIA sulfonate treatment.

Inclusion Criteria:

• 1.Aged 18 years or over and under 80 years;
• 2. First-time myocardial infarction on admission;
• 3. Presence of STEMI who has successfully coronary recanalization by PCI within 12 h after the symptom onset;
• 4. Willingness to provide informed consent prior to enrollment;
• 5. Patient is able to comply with all follow-up evaluation

Exclusion Criteria:

• 1. Contraindications to performance of CMRI [pacemakers, implantable cardioverter/defibrillator devices, cardiac resynchronization therapy (CRT), claustrophobia, metal implants (joint prosthesis, et al), history of penetrative eye lesion];
• 2. Previous myocardial infarction, arrhythmia (including atrial fibrillation or bundle brunch block), significant valvular disease, and hypertrophic cardiomyopathy;
• 3. Severe heart failure (NYHA cardiac function class IV or left ventricular ejection fraction≤30%) or cardiogenic shock;
• 4. Serious impairment of renal function (glomerular filtration rate ≤50 mL/min per 1.73 m2);
• 5. Hypohepatia (elevated of alanine aminotransferase and aspartate aminotransferase serum levels);
• 6. Severe coagulopathy prior to randomization;
• 7. Malignant tumors or other life-threatening diseases with limited life expectancy <1 year;
• 8. Significant neuropsychopathic condition precluding written informed consent;
• 9. Pregnant and lactating women;
• 10. Known radiographic contrast or sodium tanshinone IIA sulfonate allergy;
• 11. Be on therapy with immunosuppressants;
• 12. Currently participated in any other investigational therapeutic or device trial;
• 13. Clinical follow-up over the next half years not possible