AbstractTreatment of glutaraldehyde‐fixed pericardium with L‐glutamic acid and storage in bacteriostatic preservatives (paraben) stably antagonizes free, reactive aldehyde groups within the fixed bioprosthetic heart valve tissue. In 63‐day subcutaneous implants in rats, the calcification rate of this treatment (13.3 ± 2 mg calcium/g wt tissue) was markedly reduced as compared to conventionally treated tissue (169 ± 24 mg/g; p<0.05). To test the influence of tissue released toxic aldehdyes on spontaneous endothelial cell ingrowth in vivo, vascular grafts (8‐cm long, 6‐mm diameter) from fixed pericardium treated with L‐glutamic acid were interposed into the carotid arteries in ten sheep. They were compared to grafts from conventionally treated pericardium implanted at the contralateral side. Following 3 months of implantation, planimetry revealed 49%± 20% of the surface of conventionally preserved pericardium to be covered with red thrombus, but only 12%± 5% in L‐glutamic acid treated pericardium (p<0.05). The ultrastructural findings of a closed endothelial cell layer on the graft surface reveals the new technique to be a promising approach towards increased biocompatibility of aldehyde‐fixed biopros