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The presistent increase of 12/15 lipoxygenase enzyme activity is correlated with uncontrolled inflammation, leading to organ dysfunction. ML351, a potent 12/15 lipoxygenase (12/15LOX) inhibitor, was reported to reduce infarct size and inflammation in a murine ischemic stroke model. In the presented work, we have applied three complementary experimental approaches, in-vitro, ex-vivo, and in-vivo, to determine whether pharmacological inhibition of 12/15LOX could dampen the inflammatory response in adult mice after Kdo2-Lipid A (KLA) as an endotoxin stimulator or post myocardial infarction (MI). Male C57BL/6 (8–12 weeks) mice were subjected to permanent coronary ligation thereby inducing acute heart failure (MI-d1 and MI-d5) for in-vivo studies. 12/15LOX antagonist ML351 (50 mg/kg) was subcutaneously injected 2 h post-MI, while MI-controls received saline. For ex-vivo experiments, ML351 (25 mg/kg) was injected as bolus after 5 min of inflammatory stimulus (KLA 1 μg/g) injection. Peritoneal macrophages (PMɸ) were harvested after 4 h post KLA. For in-vitro studies, PMɸ were treated with KLA (100 ng/mL), ML351 (10 µM), or KLA + ML351 for 4 h, and inflammatory response was evaluated. In-vivo, 5LOX expression was reduced after ML351 administration, inducing a compensatory increase of 12LOX that sensitized PMɸ toward a proinflammatory state. This was marked by higher inflammatory cytokines and dysregulation of the splenocardiac axis post-MI. ML351 treatment increased CD11b+ and Ly6Chigh populations in spleen and Ly6G+ population in heart, with a decrease in F4/80+ macrophage population at MI-d1. In-vitro results indicated that ML351 suppressed initiation of inflammation while ex-vivo results suggested ML351 overactivated inflammation consequently delaying the resolution process. Collectively, in-vitro, ex-vivo, and in-vivo results indicated that pharmacological blockade of lipoxygenases using ML351 impaired initiation of inflammation thereby dysregulated acute immune response in cardiac repair.