Objective — Pioglitazone treatment in type 2 diabetes mellitus produced significant improvements in glycaemic control, plasma lipids, blood pressure and inflammation. The aim of this study was to investigate the effect of pioglitazone on systolic and diastolic function in diabetic patients.Methods and results — Forty-nine diabetic patients were included in the study.The patients had never received thiazolidinedione therapy before. Clinical and echocardiographic variables were measured. 30 mg pioglitazone were administered. The patients were followed up for six months and all the measurements were re-evaluated for comparison. Body mass index (BMI) significantly increased after treatment. Fasting glucose, HbA1c and systolic blood pressure decreased. Insulin resistance improved and the HOMA-IR index decreased after pioglitazone treatment. Mean aortic diameter, left atrial systolic and diastolic volumes significantly decreased after therapy. Among diastolic function variables mitral E wave, E/A, ejection time and pulmonary vein peak reverse flow velocity (PVA) significantly increased whereas isovolumetric relaxation time (IVRT), isovolumetric contraction time (IVCT), deceleration time, E/E’ and pulmonary vein late systolic flow (PVS2) decreased after pioglitazone therapy. Among tissue Doppler variables early (E) ventricular inflow velocities measured from the tricuspid lateral annulus, the mitral septal and lateral annulus, the anterior, inferior and posterior free wall significantly increased. Late (A) ventricular inflow velocities measured from the anterior, inferior free wall and the mitral septal annulus also increased.Conclusion — Pioglitazone treatment in type 2 diabetes mellitus produced significant improvements in measures of glycaemic control and diastolic ventricular function.