The goal of this clinical trial is to investigate whether morphine modulates the functions of the stellate ganglion to reduce myocardial ischemia/reperfusion injury in AMI patients. It will also assess the safety of injecting morphine around the stellate ganglion via ultrasound guidance. The main questions it aims to answer are:

1. Does morphine regulate stellate ganglion function to reduce myocardial ischemia/reperfusion injury in AMI patients?
2. What medical problems do participants experience when receiving injected morphine around the stellate ganglion? Researchers will compare morphine to a placebo saline (as a control group) to determine whether stellate ganglion infiltration with morphine effectively treats patients with AMI following primary PCI.

Participants will:

• Receive a single injection of morphine or saline around the stellate ganglion.
• Evaluate the percentage of infarct size 7 days after surgery, or at discharge if the duration is shorter than 7 days.
• Record their symptoms and any major adverse cardiovascular and cerebrovascular events within 30 days post-surgery.

Acute ST-segment elevation myocardial infarction (STEMI) patients (aged ≥18 years) planned for percutaneous coronary intervention (PCI) will be enrolled for this study. Patients with severe complications of myocardial infarction, such as uncontrollable acute left heart failure or pulmonary edema, severe cardiogenic shock after cardiopulmonary resuscitation, severe mechanical complications including ventricular septal defect, papillary muscle rupture, and rupture of the left ventricular free wall; with old myocardial infarction, or cardiomyopathy, or malignant arrhythmias controlled by antiarrhythmic drugs; with coagulation disorders due to systemic diseases and those who are currently using anticoagulants and are not suitable for injection; with allergy to opioids or with a history of opioid addiction and those participating in other clinical studies; with pregnant or breastfeeding women; with severe organ dysfunction or failure; with severe infections; with severe mental illness that cannot cooperate and those taking antipsychotic drugs or considered unsuitable for this study by the researchers will be excluded. Subjects will be randomly assigned to one of two groups: the placebo group and the morphine group. Patients in the morphine group will receive a single injection of morphine (10 mg, 10 ml) around the left stellate ganglion under ultrasound guidance before coronary artery recanalization. Moreover, the placebo group will receive a 10 ml 0.9% saline infiltration around the stellate ganglion. The percentage of myocardial infarct size is measured by MRI either 7 days after primary PCI or at discharge if the duration is shorter than 7 days as the primary outcome. The secondary outcomes include the rate of major adverse cardiovascular and cerebrovascular events, cardiac function, rehospitalization rate, and mortality within 30 days; evaluation of myocardial injury during hospitalization, including cTnI levels and ECG examinations.

Inclusion Criteria:

1. Aged ≥18 years, Male or Female.
2. Acute ST-segment elevation myocardial infarction (STEMI) patients planned for percutaneous coronary intervention (PCI). Acute STEMI is defined as: electrocardiogram shows ST-segment elevation ≥0.2 mV in two or more adjacent leads, or new left bundle branch block (LBBW).
3. Within 24 hours of the onset of infarct-related chest pain.
4. Obtaining informed consent from the patient and their family.

Exclusion Criteria:

1. Patients with severe complications of myocardial infarction, such as uncontrollable acute left heart failure and pulmonary edema, severe cardiogenic shock after cardiopulmonary resuscitation, severe mechanical complications including ventricular septal defect, papillary muscle rupture, and rupture of the left ventricular free wall;
2. Patients with old myocardial infarction, or cardiomyopathy, or malignant arrhythmias controlled by antiarrhythmic drugs;
3. Patients with coagulation disorders due to systemic diseases and those who are currently using anticoagulants and are not suitable for injection;
4. Patients allergic to opioids or with a history of opioid addiction and those participating in other clinical studies;
5. Pregnant or breastfeeding women;
6. Patients with severe organ dysfunction or failure, such as liver failure, renal failure, and respiratory failure;
7. Patients with severe infections;
8. Patients with severe mental illness that cannot cooperate and those taking antipsychotic drugs;
9. Other patients considered unsuitable for this study by the researchers.