In recent years, there has been a worsening shortage of small and intermediate-sized aortic and pulmonary allografts for use as right ventricular-to-pulmonary artery conduits in infants and children. However, there is a surfeit of large pulmonary and aortic allografts from adult donors. The feasibility of reducing a large allograft to a more useful size was examined using human pulmonary and aortic allografts. Eleven pulmonary allografts (11 to 26 mm in diameter) and nine aortic allografts (5 to 27 mm in diameter) were studied. Valve competence before downsizing was tested with a column of saline to a static pressure equivalent to the normal pulmonary pressure (20 mm Hg). Regurgitant flow was measured for 15 minutes. One complete cusp of the valve was excised, together with a longitudinal strip of the arterial wall. A bicuspid valved conduit was created by suturing the allograft longitudinally. The diameter of the bicuspid valve was measured with a dilator. A nomogram was constructed that predicts the size of the bicuspid allograft based on the size of the original allograft. The competence of the bicuspid allograft was tested and the regurgitant flow was compared with that of the original tricuspid allograft. The transvalvular systolic pressure gradient was measured with the bicuspid allograft placed in a pulsatile extracorporeal perfusion circuit at a flow rate of 1 L/min and a mean pressure of 20.5 +/- 2.6 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)