In human, pulmonary arterial pressure (Ppa)increases with age, and this has been attributed to pulmonary vascular resistance (PVR). The aim of this study was to investigate the effect of age on pulmonary hemodynamics and haemorheological properties in healthy Beagle dogs. Fourteen healthy experimental Beagles from two age groups were included, 8 young dogs aged 10 months to 5 years (mean: 2.7 years) and 6 old dogs aged 8 to 15 years (mean: 12.1 years). Haematology and biochemistry were measured. Cardiac catheterization was performed under general anaesthesia. Systolic, mean, diastolic and occluded Ppa were measured from the distal port of a pediatric thermodilution Swan-Ganz catheter inserted transcutaneously in the left jugular vein and positioned in the pulmonary artery under fluoroscopic guidance, while right atrial pressure (Pra) was measured from its proximal port. Cardiac output (CO) was determined by the thermodilution technique. Stroke volume (SV), PVR, pulmonary arterial pulse pressure (PP) and compliance (C) were calculated. Haematology and biochemistry measurements were not different between the 2 groups. Systolic, mean and diastolic Ppa were higher in old dogs (respectively 30,62,1mmHg, 19,31,8mmHg and 13,41,4mmHg) compared with young dogs (respectively 21,41,5mmHg, 13,71,2mmHg and 9,51,1mmHg). This increased Ppa was accompanied by higher PP and PVR, and lower C. Occluded Ppa, Pra, CO, SV and heart rate were not different between the 2 groups. Systolic (r=0,72; p<0,005), diastolic (r=0,46; p<0,05), mean Ppa (r=0,61; p<0,01), C (r=0,69; p<0,005) and PVR (r=0,78; p<0,005) were correlated with age while C and PVR were inversely correlated (r=0,71; p<0,005). Results of the present study show that a mild increase of Ppa is observed in old Beagle dogs compared to youngBeagle dogs, and thatfactors implicated are PVR and C.