Inclusion Criteria: the enrolled subjects must meet all of the following criteria:  Aged 18-75 years old (inclusive); Diagnosed with anterior STEMI within 6h of symptom onset: (1) ischemic chest discomfort; (2) electrocardiogram (ECG) with ST elevation ≥0.2 mV in 2 or more contiguous precordial leads (one of which should be V2, V3, or V4); Sign the informed consent form.  Exclusion Criteria: subjects who meet any one of the following criteria are excluded from the study:  Ventricular fibrillation, cardiogenic shock, Killip III-IV grade; Sinus bradycardia (heart rate sustained <60 beats/min), PR interval> 240ms or II-III degree atrioventricular block; Continuous systolic blood pressure <120mmHg; Severe breathing difficulties, aterial blood oxygen saturation <92%; Thrombolytic therapy has been performed before the first medical contact in the hospital; Consciousness disorder or past cerebrovascular disease; Previous history of myocardial infarction or PCI/CABG treatment; Known severe liver and kidney dysfunction; Known allergy to dexmedetomidine; CMR contraindications: such as claustrophobia, pacemaker or ICD implantation; Pregnant or lactating women; Malignant tumor or expected survival time <1 year; Any condition which in the opinion of the investigator would make it unsafe or unsuitable for the patient to participate in this study (eg, poor compliance, inability of the patient to comply with study procedures and/or follow up); Participate in other randomized controlled studies at the same time.