Study on some ratios of Doppler echocardiography of 93 patients under 15 years old with a isolated ventricular septal defect, by comparision with control group showed that: 55% patients had pulmonary systolic hypertension, of these 23% severe pulmonary systolic hypertension. There was close correlation of pulmonary artery systolic pressure and: Diameter of defect, and the ratio of pulmonary to systemic flow (Qp/Qs). There was no correlation of pulmonary artery systolic pressure and: Pulmonary artery diameter; Peak gradient between right ventricular and pulmonary artery; Mean gradient between right ventricular and pulmonary artery.