Diastolic dysfunction may be the earliest marker of a diabetes-induced heart muscle disease which leads to the progressive development of cardiac failure. Left ventricular diastolic function was indirectly assessed using pulsed wave Doppler ultrasound mitral-flow velocities in 20 normotensive patients with a new diagnosis of type 2 diabetes mellitus, normal cardiac function and no evidence of coronary artery disease and in 16 age-matched normal subjects. Peak velocities of early (E) and late (A) left ventricular filling were measured. The median (interquartile ranges) peak E/A ratio was significantly reduced in the diabetic group 0.96 (0.8-1.2) vs 1.2 (1.1-1.3), P < 0.01. Despite improvements in glycaemic control over 3 months, HbA1c 9.9% (7.6%-10.5%) to 7.4% (6.5%-7.9%), P < 0.001, maintained at 6 months, HbA1c 7.0% (6.4%-7.3%), there were no changes in the E/A ratio, 0.96 (0.83-1.15) and 0.95 (0.83-1.17), respectively. Furthermore, there was no correlation between percentage change in HbA1c and E/A ratio over 6 months. The results of this study suggest that in patients with type 2 diabetes mellitus and normal systolic function, diastolic function was impaired at diagnosis and was not affected by an improvement in the glycaemic control.