In a prospective observational study very low birth weight preterm infants clinically suspected to have a patent ductus were subjected to echocardiography. Two different observers each performed an echocardiographic and Doppler ultrasound examination within 30 minutes of the other. There were three total observers and 54 measurements (27 pairs) overall in 19 infants. Parameters measured were: left atrium-to-aortic root-ratio, diameter of the patent ductus arteriosus at its narrowest part, the left-ventricular-preejection-period-to-ejection-time-ratio and the ratio of the velocity time integrals in the large vessels. The repeatability of echo findings was calculated using statistical methods such as repeatability coefficient, repeatability index, and a confidence step analysis. The repeatability of echo findings to diagnose left to right shunt through a ductus arteriosus was poor, with the repeatability coefficients for different parameters ranging from 11 to 26%.