Aims: Although chloroquine and diclofenac are not cardiovascular drugs, their chronic administration may trigger cardiotoxicity. We, therefore, evaluated the cardiotoxic impact of diclofenac in chloroquine-treated adjuvant arthritic rats and the protective role of Rho-kinase inhibitors. Methods: 90 male rats were equally distributed into 9 groups including control. Arthritis was induced by S.C injection of Complete Freund's adjuvant in hind paw plantar surface. Arthritic rats were subdivided into 8 groups, orally treated with: no drug, chloroquine (50 mg/kg), diclofenac sodium (1 mg/kg) and chloroquine + diclofenac. To study the role of Rho-kinase in chloroquine/diclofenac-triggered cardiotoxicity, four arthritic groups were also co-treated with Rho-kinase inhibitors (fasudil or atorvastatin) along with diclofenac and chloroquine + diclofenac. Key findings: All treatments significantly elevated serum cardiac injury and dysfunction markers as well as left ventricular malondialdehyde but depleted antioxidants with the greatest effect in the combination group. Chloroquine and/or diclofenac; in particular, their combination shifted the balance between left ventricular pro- and anti-apoptotic proteins towards myocardial apoptosis. Surprisingly, treatment with diclofenac or chloroquine/diclofenac markedly up-regulated cardiac RhoA and Rho-kinase1. Such up-regulation was coupled with a greater increase in cardiac oxidative damage biomarkers in the combination group than in individually-treated ones. However, Rho-kinase inhibition protected against diclofenac-induced increase in myocardial oxidative damage markers. Significance: Diclofenac greatly amplified cardiac oxidative damage in chloroquine-treated arthritic rats via up-regulation of Rho-kinase1. However, Rho-kinase inhibitors provided cardioprotection against diclofenac toxicity. Overall, they could be used as safer adjuvants to diclofenac during the treatment of rheumatoid arthritis with chloroquine.