A magnetic sensor elastometry device (MSED) and a method to perform the whole blood thromboelastography assay. It contains key components, including sample cuvette, detecting head, rotating disc, optical motion detector, and etc; and measures viscoelasticity of whole blood samples. The device optically monitors the physical motion of the magnetically driven rotating disc immersed in the blood sample. The thromboelastograph is recorded by the optical motion detector reading high pulse counts through a gated time window passing through the rotating disc. The device also includes a microcontroller and its embedded firmware to perform the functions of driving the rotating magnetic disc, generating high-frequency pulses, controlling the data pulse time window, as well as handling the user's interface, data analysis, and maintaining communication with an external computer.