According to an example, a blood viscosity value of blood flowing through a blood vessel may be calculated by detecting a deformation of a blood vessel due to a pulsatile wave of blood flowing through the blood vessel, determining a pulsatile wave velocity of the pulsatile wave based upon the detected deformation, and calculating the blood viscosity value of the blood flowing through the blood vessel based on a predetermined relationship between blood viscosity and the determined pulsatile wave velocity.
