Sodium-glucose cotransporter 2 (SGLT2) inhibitors are strongly recommended in patients with heart failure, regardless of the presence of diabetes mellitus. A 74 year-old woman with a reduced left ventricular ejection fraction and diabetes mellitus (the types were unknown), receiving insulin and SGLT2 inhibitor, was hospitalized for altered consciousness with systemic hypotension. Upon admission, she was diagnosed with cardiogenic shock due to diabetic ketoacidosis. Intensive fluid resuscitation under Impella CP support successively improved her metabolic acidosis, preventing worsening pulmonary congestion by mechanically unloading the heart. After hemodynamic stabilization, she was diagnosed with type 1 diabetes mellitus for the first time. She was discharged on day 54 and was followed for 6 months without any recurrences. We must remain vigilant regarding the risk of diabetic ketoacidosis in patients using SGLT2 inhibitors, particularly those on insulin therapy or with diabetes mellitus of unknown types. Impella device shows promise as a circulatory support system in alleviating the left ventricle's workload and averting exacerbated pulmonary congestion, especially in cases where patients necessitate aggressive fluid replacement therapy, such as in the treatment of diabetic ketoacidosis concurrent with compromised cardiac function.