BACKGROUND Experience in Vellore suggests that pulmonary arterial hypertension develops at an earlier age in Indian patients with secundum atrial defects than it does in westerners. We examined the haemodynamic data on patients with secundum atrial defects to determine whether this was also true in Delhi. METHODS We analysed the data on 461 patients with secundum atrial defects, grouping them according to their pulmonary (Qp) and systemic (Qs) flow rates as well as the ratio of pulmonary to systemic systolic pressure (Pap/Sap) into 4 groups: [table: see text] RESULTS There were 8 (2%) patients in group 1, 282 (61%) in group 2, 124 (27%) in group 3, 28 (6%) in group 4a and 19 (4%) in group 4b. Of the 19 patients in group 4b, 6 (1%) were below 20 years of age and 13 (3%) above 20 years. CONCLUSIONS Our findings indicate that obstructive pulmonary arterial hypertension does not develop early in patients in Delhi.