We investigated the source of intravascular fat in systemic organs (brain, heart, and kidney) after massive pulmonary fat embolism during cemented arthroplasty. We used a bilateral cemented arthroplasty (BCA) in anesthetized mongrel dogs that simulates a cemented total-hip replacement procedure. We hypothesized that deformable fat globules could pass through the lung vasculature under high pulmonary artery pressure (Ppa). Using quantitative morphometry, we showed that the size of pulmonary vessel occluded by fat decreased from 12.8 +/- 15.2 microns 1 min after BCA to 4.9 +/- 5.1 microns at 120 min after BCA (p < 0.01). Ultrastructural studies demonstrated no evidence of acute inflammation around fat-occluded pulmonary vessels 3 h after BCA. Intravascular fat was found in all brain, heart, and kidney specimens examined 3 h after BCA (n = 6). No anesthetized animal in the "sham" (no BCA) group (n = 3) had intravascular fat at the same time period. Radiolabeled microspheres (15 microns diameter) did not reach the systemic circulation (< 1% nonentrapment) under the high Ppa after BCA. No patent foramen ovale was found in any dog at postmortem examination. We conclude that fat globules can traverse the pulmonary circulation within 3 h of orthopedic surgery. The difference between solid microspheres and fat in transpulmonary passage suggests that the composition, perhaps the deformability, of embolic material influences the lung's filtering capacity.