Hemodynamic parameters of six groups of guinea-pig hearts were studied by the working heart technic of Neely. Three groups were respectively perfused with: Krebs-Henseleit, purified native hemoglobin 1gm/dl and hemoglobin conjugated to dextran benzene tetracarboxylate 1 gm/dl. Three other groups were perfused under the same conditions except that after 30 mn of perfusion, 10 mn of total ischemia were produced followed by 30 mn of reperfusion with the previous solutions. All solutions contained 10 g/l of BSA. Hearts perfused with Hb solutions without ischemia or after ischemia show better parameters than with Krebs-Henseleit. These observations suggest that contrary to previously published results, purified Hb and more, dextran-BTC-Hb appear to be perfusable and are less deleterious for heart than saline without hemoglobin.