We investigated the effects of dobutamine therapy on myocardial function in premature infants. Left ventricular performance was assessed by measuring left ventricular systolic time intervals: rate-corrected pre-ejection period (PEPI), rate-corrected left ventricular ejection time (LVETI), and pre-ejection period to left ventricular ejection time ratio (PEP/LVET) which was obtained by echocardiography. Measurements were performed in 17 hemodynamically unstable premature infants who had an elevated PEP/LVET ratio before and 30 min after starting dobutamine infusion (10 micrograms/kg.min). Dobutamine infusion resulted in a significant decrease in PEPI (from 108 +/- 16 [SEM] to 95 +/- 17 msec; p less than .01) and in PEP/LVET ratio (from 0.55 +/- 0.16 [SEM] to 0.45 +/- 0.17; p less than .01), and in a significant increase in LVETI (from 255 +/- 15.7 [SEM] to 264 +/- 16.2 msec; p less than .01). Heart rate increased significantly from 146 +/- 17 (SEM) to 163 +/- 16 beat/min; p less than .01. Mean arterial pressure increased in 12 of 14 infants. These results show that dobutamine enhances left ventricular performance in premature infants who have depressed left ventricular function.