In acute coronary syndromes inflammatory process plays an important role in atherosclerotic plaque instability. Our aim was to evaluate the presence and distribution of vulnerable plaques and inflammatory infiltrates in patients who died of acute myocardial infarction in comparison to patients who died of non-coronary heart disease. We analyzed pathologic studies of the heart of 68 patients who died of acute myocardial infarction and 15 patients who died of non-coronary heart disease. The presence of thrombus, intraplaque hemorrhage, endothelial rupture and inflammatory infiltrates were registered. In patients who died of myocardial infarction, we found thrombus in 73.5% of the involved arteries and in 28.7% of the non involved (p < 0.0001). Intraplaque hemorrhage was found in 70.5% of involved arteries and in 39.7% of the non involved (p < 0.0001); endothelial rupture in 29.4% of involved arteries and in 3.7% of non involved arteries (p < 0.0001). There was no difference in the presence of inflammatory infiltrates (76.5% versus 68.4%). Comparing with patients who have died of non-coronary heart disease, the presence of thrombus was significantly higher (73.5% vs. 13.3%; p < 0.0001), as well as the presence of intraplaque hemorrhage (70.5% vs. 0%; p < 0.0001) and of inflammatory infiltrates in atherosclerotic plaques (76.5% vs. 46.6%; p = 0.021). In patients who died of acute myocardial infarction we observed plaque instability and inflammatory activity, not only in the infarct related artery but also in the non involved arteries.