Systolic time intervals (STI) were recorded in 33 newly diagnosed non-insulin-dependent diabetics (19 men, 14 women, aged 44-64 years) before and after 3-8 months' dietary therapy. The mean (+/- SD) fasting blood glucose was 11.1 +/- 2.6 mmol/l before treatment and 7.8 +/- 1.8 at the second examination (p less than 0.001). Concomitantly with the decline in blood glucose concentration, the heart rate corrected pre-ejection period (PEP) decreased from 139 +/- 11.9 to 135 +/- 14.4 msec (mean +/- SD) (p less than 0.05), the heart rate corrected left ventricular ejection time (LVET) increased from 400 +/- 15.1 to 410 +/- 20.7 msec (p less than 0.0025) and the PEP/LVET ratio decreased from 0.39 +/- 0.06 to 0.36 +/- 0.06 (p less than 0.005). When the diabetics were divided into two groups according to the degree of the decline in blood glucose concentration, only those whose fasting blood glucose decreased by greater than or equal to 3 mmol/l showed significant changes in STI. No significant changes were observed in the mean heart rate or systolic blood pressure during the treatment. Cardiac dysfunction occurring in untreated non-insulin-dependent diabetics may be caused by metabolic factors and it may be reversed at least partially by correction of hyperglycemia.