Preliminary hemorheologic studies using clinical filtration techniques on blood cell suspensions have suggested that changes in erythrocyte (RBC) deformability occur during left ventricular assist system (LVAS) support. In the biophysics literature, it is generally accepted that the elastic properties of the RBC membrane complex affect the microcirculatory deformability of the whole cell (cytoplasmic pathologies excepted). This paper compares single cell measurements of the surface shear elastic modulus, mu, of the RBC membrane complex (determined using micropipette aspiration) to available clinical filtration pressure data during Novacor LVAS support, over 33 and 126 days in four patients.