The current use of doxorubicin is regarded as an absolute contraindication for hyperbaric oxygen (HBO2) therapy because of the increased risk of cardiotoxicity. The aim of this study was to investigate whether additional exposure to HBO2 during the course of doxorubicin treatment would further increase the cardiotoxicity of doxorubicin in rats. Female Wistar rats were treated with either HBO2 (n = 10) or doxorubicin (n = 8) or a combination of both treatments (n = 10) for 4 consecutive weeks and followed up for an additional 4 weeks. Cardiomyopathy was evaluated using two-dimensional and M-mode echocardiography at baseline, at the fourth, sixth and eighth weeks, and by histopathological investigation of the rat hearts at the eighth week. Doxorubicin treatment significantly reduced ejection fraction and fractional shortening (P < 0.001) and caused severe histopathological injury (P < 0.05) indicating development of cardiotoxicity. Although the combination of doxorubicin and HBO(2) also markedly reduced ejection fraction and fractional shortening (P < 0.001), this reduction was significantly less than that of doxorubicin treatment (P < 0.05). HBO2 therapy also attenuated doxorubicin-induced histopathological changes in rat hearts (P < 0.05). HBO2 alone did not alter echocardiographic parameters or histopathological findings (P > 0.05). In conclusion, HBO2 therapy does not potentiate doxorubicin-induced cardiotoxicity in rats. Cardioprotection conferred by HBO2 against doxorubicin warrants further investigation.