A technique is provided for computing or monitoring blood viscosity. The technique includes measuring a cross sectional area of a arterial segment and a volumetric flow rate of blood flowing through the arterial segment at two or more locations, estimating a compliance transfer function from blood measurements to scale the arterial cross sectional area into a pressure waveform, deriving a transmission line model of the arterial segment based on the cross sectional area, as scaled by the compliance transfer function, of the arterial segment at the two or more locations and the volumetric flow rate of blood at the two or more locations. The technique also includes computing the blood viscosity based on the transmission line model.