Orrem HL, et al. - In this post hoc analysis of the LEAF trial (LEvosimendan in Acute heart Failure following myocardial infarction) evaluating 61 patients developing heart failure (HF) within 48 hours after percutaneous coronary intervention-treated ST-elevation myocardial infarction, researchers tested the validity of their hypothesis that the degree of complement activation reflects severity of HF after acute myocardial infarction. They found that in cases of acute ST-elevation myocardial infarction complicated by HF, the cardiogenic shock was distinguished from non-shock by the presence of complement activation. Furthermore, complement activation showed correlation with regional contractility and endothelial cell activation. These data suggest that complement plays a pathogenic role in this condition.