This is a Phase 3 prospective, blinded, randomized, placebo controlled, international multicenter study. Subjects with STEMI will be enrolled in the ambulance if they meet all eligibility criteria. These subjects will be evaluated by (para)medics who transport the subjects to the participating hospitals in Europe and North America. Hospitals and ambulance services with experience in ambulance studies will be selected. Each subject will receive a single subcutaneous injection containing either Disaggpro(tm) zalunfiban Dose 1 (0.110 mg/kg) or Disaggpro(tm) zalunfiban Dose 2 (0.130 mg/kg) or placebo

Subjects will be screened in the ambulance based on the information available; those fulfilling the eligibility criteria who have provided verbal witnessed/short written/Exception from Informed Consent Requirements (EFIC) process informed consent will be randomized and enrolled in the study. Following a single weight-based dose of subcutaneous study drug administered by the ambulance staff, the patient will be transferred to the clinical site PCI center for angiography and intervention.

Regular standard of care is performed from the provision of informed consent through the last study mandated subject visit. Concomitant medications will be recorded. Treatment with IV P2Y12 antagonists or other αIIbβ3 receptor before PCI/angiography is prohibited. Demographics, concomitant medications, vital signs, and medical history will be collected in the CRF. Adverse events, bleeding events and injection site reactions will be collected. Angiography and PCI details will be recorded. Full written informed consent will be obtained. Additional blood samples for safety will be collected at 1, 6, 24 and 72 hours (or hospital discharge) post-PCI/angiography. Blood samples for high-sensitive cardiac troponin T (upon arrival and 24 hours post PCI/angiography) and NT-ProBNP (24 hours post PCI/angiography) will be assessed by central laboratory. Follow up phone contacts will occur at 30 days to report AEs, bleeding events, and injection site reactions, and 12-months to record mortality, and hospitalizations for heart failure or atrial fibrillation, and [in the event of stroke], 90 days (±2 weeks) to record the stroke disability.

Angiography/PCI data and ECGs will be evaluated at independent Core Laboratories. An independent, blinded Clinical Events Committee will provide central adjudication of all clinical endpoint events. A DSMB will examine the safety data in an ongoing manner and to alert the Steering Committee in case of clinically concerning safety issues that should lead to consideration of altering the trial, and can recommend modification of the study protocol based on pre-specified rules.

The duration of participation for each subject will be 12 months (± 1 month), including enrollment, study drug administration, hospitalization, and phone contact follow-up at 30 days (+ 7 days) and 12 months (± 1 month).

Inclusion Criteria:

1. Males aged ≥18 years or post-menopausal or surgically sterile females ≥50 years or ≥55 years (for Czech Republic study sites only).
2. Weight (by history) between 52 and 130 kg.
3. Subjects with STEMI, presenting with persistent ischemic chest pain (>10 minutes) and new ≥2 mm ST-segment elevation in two adjacent ECG leads, in whom the total duration of symptoms is 4 hours maximum. If time of symptom onset is uncertain, the cardiologist may be contacted to confirm inclusion criteria.
4. Exception from Informed Consent Requirements (EFIC) process, verbal witnessed/ short written informed consent, or written informed consent signed by subject or legally authorized representative/independent witness will be obtained in the acute phase by (para)medics, according to local applicable legal regulations. Subject is willing and able to give informed consent. Written informed consent will be obtained as soon as the subject's clinical condition allows it.

Exclusion Criteria:

1. Cardio Pulmonary Resuscitation (CPR) for current Out of Hospital Cardiac Arrest (OHCA).

2. Presenting with systolic blood pressure <90 mmHg (confirmed on repeat assessment) and heart rate >100 beats per minute (bpm).

3. Current known active coronavirus disease 2019 (COVID-19) infection (criteria according to local guidelines).

4. Currently treated with renal dialysis.

5. Current treatment with oral anticoagulation (Vitamin K antagonists [VKA], direct oral anticoagulants [DOACs]), or thrombolytic agents.

6. Major surgery, or trauma or bleeding leading to hospitalization, within the past month.

7. Known history of ischemic or hemorrhagic stroke.

8. Known severe anemia (regular blood transfusion needed).

9. Previously enrolled in this study.

10. Participation in another clinical study with an investigational product or device within the past month.

11. Life expectancy less than one year.

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