BACKGROUND The development of hypertensive pulmonary vascular disease (HPVD) is considered a risk factor in the long-term course of patients with secundum atrial septal defects (ASD). The aim of this study was to assess the prevalence and histologic degree of HPVD and pulmonary hypertension in relation to preoperative clinical and hemodynamic data, intraoperative findings, and operative outcome in adults. METHODS Lung biopsies of 75 patients, mean age 44 +/- 14 years (18-71 years), with secundum ASD or sinus venosus defect including ten patients with partial anomalous pulmonary venous return were analyzed in accordance with preoperative and intraoperative findings as well as operative outcome. Lung biopsy was performed at the time of defect closure and was classified according to Heath and Edwards. RESULTS Structural changes of the pulmonary vasculature were found in 59% of patients; grade 3 and higher changes were present in 19%. There were no statistically significant relations between histologic findings and preoperative clinical and hemodynamic data, intraoperative findings, and operative outcome. The prevalence of moderate (32-50 mm Hg) and severe (> 50 mm Hg) systolic pulmonary hypertension was 27% and 17%, respectively. Increased systolic pulmonary arterial pressure was associated with increased pulmonary vascular resistance (p < 0.000) and patients' age (p = 0.001). Patients with a lower functional capacity had a higher prevalence of pulmonary hypertension (p = 0.011). CONCLUSIONS The prevalence of HPVD and pulmonary hypertension in adult patients with secundum ASD or sinus venosus defect is considerable. Preoperative hemodynamic data do not predict the degree of HPVD in lung biopsy. Closure is generally advised to prevent increasing pulmonary arterial pressure and decreasing functional capacity over time.