Clopidogrel exists in oral form only. As a prodrug, it has to be metabolized to the active form by cytochrome system in the liver. Both facts could lead to lower efficacy of the drug in hemodynamically unstable patients, where splanchnic and liver hypoperfusion is present. We hypothesised that clopidogrel efficacy is insufficient in patients with acute myocardial infarction and severe hemodynamic instability. Therefore we would like to compare the effect of clopidogrel in unstable STEMI patients on mechanical ventilation with stable STEMI patients.