Treatment of myocardial infarction (blood clot in the arteries of the heart) has improved after introduction of 24/7 balloon angioplasty to open the blocked artery. However, the clot itself is not routinely removed but recent data in smaller trials indicate that this might improve recovery and prognosis. In this multicenter study of 5000 patients referred to Scandinavian hospitals for myocardial infarction the investigators test the hypothesis that patients randomized to treatment with thrombus aspiration (removing the blood clot by manual suction) before conventional angioplasty will have a reduced risk of death, fewer rehospitalisations, fewer new myocardial infarctions, reduced risk of heart failure, better coronary artery flow after angioplasty and greater reduction of infarct size compared to patients randomized to conventional angioplasty alone.