A new technique is described to facilitate descending thoracic aorta replacement without the use of anticoagulants. To eliminate the need of anticoagulants, tubes and cannulae are coated with nonthrombogenic polyurethane-polyvinyl-graphite (PPG). The left heart bypass employing them can provide a dry operative field. No significant changes were observed in clotting time and prothrombin time during this nonthrombogenic left heart bypass. The following findings were observed under scanning electron microscopy: The majority of platelets were solitarily dispersed and a few platelets were aggregated in each other on the PPG-coated tube. They were uniformly spherical or spheroidal with short spiny projections and long pseudopods. Aggregations of platelets were present but metamorphoses of the platelets and formation of fibrin nets were not observed. These findings of PPG-coated tube were similar to that of uncoated polyvinyl chloride tube in heparinized left heart bypass. Moreover PPG-coated tube showed a tendency to depress transformation of platelets in early stage of thrombus formation. However, either silicone tube or uncoated polyvinyl chloride tube did not prevent transformation of platelets. The advantages of this method over conventional left heart bypass are that the anticoagulants are not required.