We investigated the acute and chronic effects of left lung autotransplantation (LLA) on the left pulmonary vascular pressure-flow (LP/Q) relationship in conscious dogs. Continuous LP/Q plots were generated in chronically instrumented conscious dogs 2 days, 2 wk, 1 mo, and 2 mo after LLA. Identically instrumented normal conscious dogs were studied at equal time points post-surgery. LLA had little or no effect on baseline systemic hemodynamics or blood gases. In contrast, compared with normal conscious dogs, striking active flow-independent pulmonary vasoconstriction was observed 2 days post-LLA. The slope of the LP/Q relationship was increased from a normal value of 0.275 +/- 0.021 to 0.699 +/- 0.137 mmHg.ml-1.min-1.kg-1 2 days post-LLA. Pulmonary vasoconstriction of similar magnitude was also observed on a chronic basis at 2 wk, 1 mo, and even 2 mo post-LLA. Pulmonary vasoconstriction post-LLA was not due to fixed resistance at the left pulmonary arterial or venous anastomotic sites. Finally, systemic arterial blood gases were unchanged when total pulmonary blood flow was directed to exclusively perfuse the transplanted left lung. Thus, LLA results in both acute and chronic pulmonary vasoconstriction in conscious dogs. LLA should serve as a useful stable experimental model to assess the specific effects of surgical transplantation on pulmonary vascular regulation.