Abstract Whereas closure of patent ductus arteriosus (PDA) with large left-to-right shunts may be required for symptomatic relief, the reason for recommending closure of small ducts is to prevent infectious arteritis, otherwise reported with an incidence of 0.45% per year. 1 Ductal division usually offers complete closure, whereas ligation has been reported to be associated with recurrences, either due to recanalization or to incomplete closure. 2–6 The true incidence of residual ductal shunting after PDA ligation has not been clearly defined, because follow-up generally has been based on auscultatory findings that have proved unreliable in identifying residual ductal shunting. 7 Because incomplete PDA ligation may necessitate reoperation or life-long infection prophylaxis, it is important to identify patients with small residual ductal flow. Color-flow mapping is a very sensitive method for the identification of PDA flow. 7–9 Consequently, color Doppler studies were performed in 31 patients who had undergone surgical PDA ligation to evaluate the incidence of residual ductal flow.