Diabetic cardiomyopathy (DC) is defined as a ventricular diastolic and/or systolic dysfunction, which is directly related to diabetes mellitus (DM) in the absence of coronary artery disease, valvular, congenital or hypertensive heart disease, and alcoholism. In this report, we present an unusual case of a patient with DC and reversible, acute left ventricular systolic dysfunction due to cardiotoxicity of hyperosmolar hyperglycaemic state (HHS).A 20-year-old male patient presented with weakness and polyuria. Physical examination and electrocardiogram were normal. Laboratory results and arterial blood gas analysis were consistent with HHS. Baseline echocardiography showed global left ventricular hypokinesis with an ejection fraction (EF) of 36%. The patient's clinical condition improved after blood glucose level normalization and echocardiography revealed progressive improvement in the left ventricular systolic function with an EF of 54% at the 5-day follow-up and an EF of 69% at the 15-day follow-up.Uncontrolled DM and hyperglycaemic crisis may result in cardiotoxicity, acute left ventricular systolic dysfunction, and DC. The pathophysiological mechanism of this phenomenon is still unclear. Blood glucose control is the most important strategy for the prevention of DC.