Background: Coronary artery remodelling and vasospasm is a complication of acute myocardial ischemia and reperfusion. The underlying mechanisms are complex, but the vasoconstrictor peptide endothelin-1 is suggested to have an important role. This study aimed to determine whether the expression of endothelin-1 and its receptors are regulated in the myocardium and in coronary arteries after experimental ischemia-reperfusion. Furthermore, we evaluated whether treatment with a specific MEK1/2 inhibitor, U0126, modified the expression and function of these proteins. Methods and findings: Sprague-Dawley rats were randomly divided into three groups: sham-operated, ischemiareperfusion with vehicle treatment and ischemia-reperfusion with U0126 treatment. Ischemia was induced by ligating the left anterior descending coronary artery for 30 minutes followed by reperfusion. U0126 was administered before ischemia and repeated 6 hours after start of reperfusion. The contractile properties of isolated coronary arteries to endothelin-1 and sarafotoxin 6c were evaluated using wire-myography. The gene expression of endothelin-1 and endothelin receptors were measured using qPCR. Distribution and localization of proteins (pERK1/2, prepro-endothelin-1, endothelin-1, and endothelin ET_A and ET_B receptors) were analysed by Western blot and immunohistochemistry. We found that pERK1/2 was significantly augmented in the ischemic area 3 hours after ischemia-reperfusion; this correlated with increased ET_B receptor and ET-1 gene expressions in ischemic myocardium and in coronary arteries. ET_B receptor-mediated vasoconstriction was observed to be increased in coronary arteries 24 hours after ischemia-reperfusion. Treatment with U0126 reduced pERK1/2, expression of ET-1 and ET_B receptor, and ET_B receptor-mediated vasoconstriction. Conclusions: These findings suggest that the MEK-ERK1/2 signaling pathway is important for regulating endothelin-1 and ET_B receptors in myocardium and coronary arteries after ischemia-reperfusion in the ischemic region. Inhibition of the MEK-ERK1/2 pathway may provide a novel target for reducing ischemia-reperfusion damage in the heart.