MyD88 is an adaptor protein critical for innate immune response against microbial infection and in certain non-infectious tissue injury. The present study examined the role of MyD88 in myocardial inflammation and injury after ischemia-reperfusion (I/R). I/R was produced by coronary artery ligation for 30-min followed by reperfusion. The ratios of area-at-risk (AAR) to left ventricle (LV) were similar between wild-type (WT) and MyD88-deficient (MyD88^-/-) mice. However, 24 hours after I/R, the ratios of myocardial infarction (MI) to AAR were 58% less in MyD88^-/- than in WT mice (14 ± 2% vs. 33 ± 6%, P=0.01). Serial echocardiographic studies demonstrated that there was no difference in baseline LV contractile function between the two groups. Twenty-four hours after I/R, LV ejection fraction (EF) and fractional shortening (FS) in WT were reduced by 44% and 62% (EF, 51 ± 2% and FS, 22 ± 1%, P<0.001), respectively, and remained depressed on the 7^th day after I/R. In comparison, EF and FS in MyD88^-/- mice were 67 ± 3% and 33±2%, respectively, after I/R (P<0.001 vs. WT). Similarly, LV function, as demonstrated by invasive hemodynamic measurements, were better preserved in MyD88^-/- compared to WT mice after I/R. Furthermore, compared to WT mice, MyD88^-/- mice subjected to I/R had a marked decrease in myocardial inflammation as demonstrated by attenuated neutrophil recruitment and decreased expression of the pro-inflammatory mediators KC, MCP-1, and ICAM-1. Taken together, these data suggest that MyD88 modulates myocardial inflammatory injury and contributes to myocardial infarction and LV dysfunction during I/R.