Recently, ultrafast ultrasound imaging has been proposed for many clinical applications. However, most operational frequencies of ultrafast ultrasound imaging are around 3.5 to 15 MHz. Currently, ultrafast 40 MHz high frequency ultrasound imaging has been developed in our Lab. High frequency ultrasound is a good choice for blood flow mapping because the backscattering signals from blood is increased with the operational ultrasound frequency according to Rayleigh scattering. In order to enhance the blood signals, clutter filter based on singular value decomposition (SVD) is considered as a suitable solution. The purpose of this study is to perform real time blood flow mapping by using a SVD-based algorithm at a frequency of 40 MHz. In vivo experiments were carried out by mice carotid artery imaging.