Cardiac rehabilitation in patients with diabetes mellitus and heart failure may be affected by anti-diabetic drugs. However, there are few reports on the effects of sodium-glucose cotransporter-2 (SGLT2) inhibitors on cardiac rehabilitation. Thus, we retrospectively investigated the patient backgrounds and effects of cardiac rehabilitation in 44 patients admitted to our hospital with heart failure and pre-existing diabetes mellitus. Our results showed that the patients tended to be older, and those who received SGLT2 inhibitors had lower systolic blood pressure and left ventricular ejection fraction on admission than those who did not. Cardiac rehabilitation significantly improved the Short Physical Performance Battery (SPPB) score in all patients, and there was no significant difference in body mass index or in body weight. There were no significant differences in SPPB score at admission, discharge, or change from admission to discharge with or without SGLT2 inhibitors. These results suggest that SGLT2 inhibitors do not affect the change in SPPB scores. SGLT2 inhibitors may thus be used safely without affecting cardiac rehabilitation while adhering to the necessary safety precautions.