Homologous blood transfusions carry risks--febrile reactions, isoimmunization incompatibility reactions and transmission of infectious diseases such as AIDS and hepatitis. Although autotransfusion techniques will reduce the need for banked homologous blood, autologous shed blood does contain various cellular fragments that may act directly as myocardial depressants. Accordingly, the myocardial muscle mechanical properties of isolated human right atrial trabeculae contracting in vitro were measured in a bath containing either blood collected in the Sorensen ATS Autotransfusion Receptal unit or arterial autologous blood. Muscles were tested randomly in each solution by measuring their isometric resting and developed forces and the mean rate of developed force at different stimulation rates (force-frequency relation). In addition, biochemical, hematologic and immunologic assays were performed on each blood specimen. Significant increases (p less than 0.05) in potassium and plasma-free hemoglobin indicated that cell disruption had occurred in blood collected in the autotransfusion apparatus; however, there was no statistically significant difference in mechanical performance between muscles contracting in either solution. From these results, the authors conclude that autotransfused blood does not directly affect human heart-muscle mechanics.