Frozen sections of lung biopsy were prepared in 30 cases of congenital heart anomalies with pulmonary hypertension, and evaluation of severity of the pulmonary vascular changes was made during the surgery. Statistically, significant difference was not found between the diagnosis made by frozen sections and those made by paraffin sections. It is concluded that rapid and accurate diagnosis of pulmonary vascular changes can be made by means of frozen section diagnosis. This method will prove to be clinically important by assisting during operation in rapid assessment of indication for total correction of congenital heart anomalies. ACTA PATHOL. JPN. 35 : 803–807, 1985.