Background and purpose: Myocardial injury following ischaemia and reperfusion has been attributed to activation and transmigration of polymorphonuclear leukocytes (PMNs) with release of mediators including oxygen-derived radicals and proteases causing damage. Experimental approach: We studied the serine protease inhibitor aprotinin in an in vivo rabbit model of 1 h of myocardial ischaemia followed by 3 h of reperfusion (MI þ R). Aprotinin (10 000 Ukg À1 ) or its vehicle were injected 5 min prior to the start of reperfusion. Key results: Myocardial injury was significantly reduced with aprotinin treatment as indicated by a reduced necrotic area (11 ± 2.7% necrosis as percentage of area at risk after aprotinin; 24 ± 3.1% after vehicle; Po0.05) and plasma creatine kinase activity (12.2±1.5 and 17.3±2.3 IU g À1 protein in aprotinin and vehicle groups, respectively, Po0.05). PMN infiltration (assessed by myeloperoxidase activity) was significantly decreased in aprotinin-treated animals compared to vehicle (Po0.01). Histological analysis also revealed a substantial increase in PMN infiltration following MI þ R and this was significantly reduced by aprotinin therapy (44 ± 15 vs 102 ± 2 PMN mm 2 in aprotinin vs vehicle-treated animals, Po0.05). In parallel in vitro experiments, aprotinin inhibited neutrophil-endothelium interaction by reducing PMN adhesion on isolated, activated aortic endothelium. Finally, immunohistochemical analysis illustrated aprotinin significantly reduced myocardial apoptosis following MI þ R. Conclusions and implications: Inhibition of serine proteases by aprotinin inhibits an inflammatory cascade initiated by MI þ R.The cardioprotective effect appears to be at least partly due to reduced PMN adhesion and infiltration with subsequently reduced myocardial necrosis and apoptosis.