The increasing use of the aortic homograft as aortic valve substitute and the limited availability of donor valves prompted us to consider the pulmonary homograft as an alternative substitute for aortic valve replacement. The aim of our study is to compare the ultrastructural and biomechanical properties of pulmonary homograft leaflets with those of their aortic counterpart and to present the early results of using the pulmonary homograft for aortic valve replacement. Light and transmission electron microscopy have shown that pulmonary homograft leaflets are thinner than the aortic with a lesser content of elastic tissue in the ventricularis layer. However there were no substantial differences in the ultrastructure. Uniaxial tensile tests were done on 69 cusps from human pulmonary and aortic valves using an Instron testing machine. The strain at 200 KPa was found to be similar for both pulmonary and aortic leaflets (8.20% +/- 2.87% versus 8.98% +/- 1.90%) cut circumferentially. Radial strips appear to be more extensible in pulmonary leaflets than in aortic (32.6% +/- 7.5% and 28.6% +/- 11.1%, respectively). The ultimate tensile strength for circumferential strips was found to be similar for both aortic and pulmonary valves (1460 +/- 857 kPa versus 1450 +/- 689 kPa), but there was relatively little difference between the radial strips (295 +/- 95 kPa versus 252 +/- 104 kPa). A total of 123 patients whose ages ranged between 13 and 78 years received either fresh antibiotic sterilized or cryopreserved pulmonary homografts for aortic valve replacement. The pulmonary homograft was inserted in place of the patient's diseased aortic valve by using one of two different techniques: freehand in the subcoronary position or as a "short cylinder" inside the aortic root. There was three hospital deaths (2.43%; 70% confidence limits = 1.08% to 4.83%). Cumulative follow-up was 184 patient-years (range 1 to 39 months). All surviving patients have been followed up with serial color flow Doppler echocardiography. There were no late deaths. Actuarial late survival was 97.5% (70% confidence limits = 95.7% to 98.6%) at 3 years. Four patients (2.2%/pt-yr) underwent reoperation because of severe aortic regurgitation (1, 4, 12, and 15 months after the operation) because of technical problems (mismatch in size between the pulmonary homograft and aortic anulus) in three patients and probably because of graft rejection in one patient. At 3 years the actuarial rate of freedom from reoperation was 95.5% (70% confidence limits = 92.7% to 97.3%). Mild aortic regurgitation has been detected in three patients (2.6%). No patients incurred thromboembolic episodes or infective endocarditis.(ABSTRACT TRUNCATED AT 400 WORDS)