Transcatheter closure of patent ductus arteriosus (PDA) with coils is accepted as an alternative to surgical ligation. We evaluated whether flow gradient across PDA, obtained by Doppler echocardiography, can aid in selecting coils for percutaneous ductal occlusion. 79 consecutive patients with PDA, who underwent successful percutaneous coil occlusion were retrospectively reviewed. Patients with other structural heart disease and pulmonary hypertension with right-to-left shunt were excluded. Echocardiogram and cardiac catheterization were done in all patients. Gianturco (Occluding Spring Emboli; Cook, Bloomington, IN) non-detachable coils of 0.038 and 0.052-inch core sizes were used for ductal occlusion. Trough diastolic gradient was correlated with the size and the number of coils used. Mean age was 8.6 years (range 1.3 to 27 years); 24 males and 55 females; PDA diameter ranged from 1.3 to 4.5 mm. Number of coils used varied from 1 to 4. Echocardiography measured PDA size was 2.5 ± 0.6 mm and significantly differed from angiographically measured size 2.9 ± 0.6 mm (P = 0.05). End diastolic gradient below 38 mmHg predicted use of multiple coils or coils with larger surface area. End diastolic gradient correlated inversely with total surface area of the coils, which indirectly predicted size and number of coils. Thus, the prediction of the size and the number of coils for PDA occlusion can be assisted by the trough diastolic gradients of PDA.