TK-129 is an orally active, low-toxicity, potent KDM5B inhibitor (with high affinity; IC 50 =44 nM). TK-129 exerts cardioprotective effects by inhibiting KDM5B and blocking the KDM5B -associated Wnt pathway. TK-129 reduces ang II-induced activation of cardiac fibroblasts in vitro and reduces isoprenaline-induced myocardial remodelling and fibrosis in vivo. TK-129 can be used in studies of cardiovascular disease.