Abstract BACKGROUND AND PURPOSE The multi-tyrosine kinase inhibitor sunitinib malate is associated with cardiotoxicity through inhibition of 5’adenosine monophosphate protein kinase (AMPK) signalling. Here we demonstrate the cardioprotective properties of metformin limiting the adverse cardiotoxic effect of sunitinib. EXPERIMENTAL APPROACH Heart rate (HR), left ventricular developed pressure (LVDP), coronary flow (CF), infarct size, and phosphorylated-AMPKα levels were measured in the rat Langendorff hearts perfused with 1 µM sunitinib ± 50 µM metformin ± 1 µM human equilibrative nucleoside transporter inhibitor S-(4-Nitrobenzyl)-6-thionosine (NBTI). Isolated cardiac myocytes were incubated with 1 µM sunitinib ± 50 µM metformin ± 1 µM NBTI to determine the live cell population levels. Human hepatoma G2 (HepG2) and promyelocytic leukemia (HL-60) cells were incubated with 0.1-100 µM sunitinib ± 50 µM metformin to determine the cell viability. KEY RESULTS Sunitinib significantly increased the infarct size and decreased the LVDP, while the p-AMPKα level declined. In the cardiac myocytes study, treatment with sunitinib decreased the cell viability. Co-administration of metformin abolished these cardiotoxic effects of sunitinib. Co-administration of NBTI (1 µM) inhibited the cardioprotective effects of metformin. Anti-cancer properties of sunitinib and metformin was recorded using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. MTT revealed that co-administration of metformin with sunitinib decreased sunitinib’s antiproliferative properties, evidenced by an increase in EC50 concentration value when compared to sunitinib monotreatment in in-vitro HepG2 and HL60 cell lines. However, metformin co-administration did not inhibit sunitinib’s properties CONCLUSIONS AND IMPLICATIONS This study highlights the novel cardioprotective properties of metformin via AMPK during sunitinib-induced cardiotoxicity.