The effects of the metabolic changes of type 2 diabetic patients on ventricular function, especially diastolic ventricular function were investigated. An examination was performed before and after treatment of 18 diabetic patients divided into 3 groups: insulin therapy, oral hypoglycemic drugs and diet therapy (6 patients each). The results indicated that both systolic and diastolic ventricular dysfunctions observed were improved by the correction of hyperglycemia. Therefore it is necessary to treat diabetes mellitus as early as possible for the prevention of both cardiac dysfunction and microangiopathy.