A nonimaging pulsed Doppler technique was used to grade the magnitude of flow in left-to-right shunting ductus arteriosus. The results were compared with those obtained with a color Doppler flow mapping technique. The correlation between the grading results by these two methods was 0.91 (p less than 0.01). To determine hemodynamic influence of left-to-right shunting ductal flow, simultaneous measurements of Doppler-derived cardiac output were done. Results showed significantly higher cardiac output in infants with grade III shunting than in infants with grade 0 and grade I shunting. The nonimaging pulsed Doppler ultrasound technique used in the present study proved to be a clinically useful and accurate grading system of left-to-right shunting at the ductal level. The simple grading system with nonimaging Doppler is a valuable adjunct to the color Doppler flow mapping technique. It allows a regular evaluation of ductal flow as well as cardiac output.