Left ventricular function was evaluated in 24 women who developed impaired glucose tolerance only during their pregnancy, i.e. patients with gestational diabetes. The results were compared with those of 25 normal pregnant women and with those of 17 pregnant women with clinical diabetes. The method of systolic time intervals was applied. At the third trimester of pregnancy, both the women with overt diabetes and those with gestational diabetes, when compared with normal pregnant subjects, had a more prolonged pre-ejection period (PEP) and a shorter left ventricular ejection time (LVET) and, consequently, a higher PEP/LVET ratio. Five weeks after delivery, abnormalities of systolic time intervals persisted in patients with clinical diabetes, but there were no differences at this time between patients with gestational diabetes and those in the control group. It is concluded that when a cardiac load is superimposed on patients who develop diabetes only under conditions of stress, as in pregnancy (gestational diabetes), abnormalities of myocardial function appear, which revert to normal when the stressful event is removed.