In order to evaluate post-embolic pulmonary gas exchange responses to exercise, we studied 7 patients who had previously suffered from an acute pulmonary embolism but were presently free from clinical and functional signs of cardiorespiratory diseases. Patients came to the laboratory on two occasions, 30 and 120 days following the episode of acute embolism, respectively, and performed an incremental ramp exercise test up to the maximum attainable workload. On both occasions, the dead volume/tidal volume (VD/VT) ratio at rest increased. During the first exercise test performed 30 days after the acute pulmonary embolism, mean VD/VT decreased from a resting value of 62.5% to 38.6% at the maximum workload. During the second exercise test, VD/VT decreased, at the same workload, from 71.3% to 35.5%. There was no significant difference in exercise-related VD/VT decrease between the two exercise tests. The results suggest that in patients who have suffered from an acute pulmonary embolism, a considerable pulmonary blood flow redistribution may occur during incremental ramp exercise performed 30 and 120 days after the acute event.