Abstract Body: Ferroptosis is an iron and lipid peroxidation dependent form of cell death. It has been implicated in ischemia/reperfusion injury, heart failure, and doxorubicin (Dox)-induced cardiotoxicity (DIC). While Wingless-type family member (Wnt) pathways are crucial for heart development and remodeling, the role of Wnt5a in regulating ferroptosis in cardiac cells and its relevance to DIC remain unclear. In the present study, we investigate the role of Wnt5a signaling in cardiac ferroptosis and its implication in cardio-oncology. We observed an increase in Wnt5a secretion in H9C2 cardiac cells upon treatment with ferroptosis inducers such as ferric ammonium citrate (FAC 2 mM) and RSL3 (20 nM). Live/Dead viability analyses in cultured mouse cardiomyocytes (CMs) and cardiac fibroblasts (CFs) revealed that the Wnt5a antagonist BOX5 (100 µM) attenuated ferroptosis induced by FAC or RSL3 in both CMs and CFs. Similarly, FAC- and RSL3-induced ferroptotic death rates were reduced in CMs from Wnt5a conditional knockout (cKO) mice. Recombinant Wnt5a (rWnt5a) induced CM death in a dose-dependent manner (5, 7, 10 µg/ml) and was partially prevented by Fer-1 (10 µM), a selective ferroptosis inhibitor. Moreover, rWnt5a (10 µg/ml) also effectively induced CF ferroptosis which was inhibited by Fer-1. rWnt5a and its mimicking peptide Foxy5 also modulated the sensitivity to various ferroptosis inducers. Furthermore, FAC-, RSL3- and rWnt5a-induced ferroptosis were attenuated in CMs from frizzled 2 receptor cKO mice. We further delineated the role of Wnt5a upregulation in Dox-induced ferroptosis and the development of DIC. In a chronic DIC mouse model, Wnt5a upregulation in the heart correlated with left ventricular dysfunction which was abrogated in Wnt5a cKO mice. Live/Dead viability analyses showed that Dox induced ferroptosis which was partially prevented by Fer-1 in CMs. Inhibition of the Wnt5a pathway by BOX5 led to a decrease in the rate of Dox-induced ferroptosis, while the sensitivity to ferroptosis was enhanced by rWnt5a. Our study has shown for the first time that the production and secretion of Wnt5a in an autocrine and/or paracrine manner promotes ferroptosis in CMs and CFs. Wnt5a is likely to be a critical mediator of Dox-induced ferroptosis and cardiotoxicity.