Patient-specific blood flow simulation in human arteries has emerged as a powerful research tool to noninvasively quantify unsteady flow and pressure inside the vessel and wall shear stress (WSS) distribution on inner wall. The attractive advantages include (1) the low cost of facility, personnel, and supplies; (2) the fully human subject protection; (3) the amenability to perform parametric analysis, and (4) the direct human subject results. Radiological scanning and animal model experimentation cannot compete with these advantages to achieve similar results with the same investment. We have recently developed a unique computational platform for patient-specific computational hemodynamics (PSCH) based on clinical CT/MRI imaging information through unified mesoscale modeling using lattice Boltzmann method (LBM) for both image processing and fluid dynamics together with the emerging GPU (graphic processing unit) parallel computing technology. The PSCH computational tool, named as InVascular, is featured with easy implementation and fast computation. The LBM solves a level set equation for image segmentation from CT or MRI imaging data and extracts the boundary information. The obtained patient-specific vessel geometry, volumetric ratio of solid versus fluid, and the orientation of the boundary are then seamlessly fed to the next step for solving unsteady pulsatile flow. From CT/MARI images to in vivo flow, pressure, and WSS quantification, there are no data transformation and software involved thus the computation can be efficiently accelerated by GPU technology. It has been estimated that a typical cardiac simulation of blood flow in a human artery can be completed within 30 minutes. This talk is about the computational methodology, the modeling techniques, validation, and three medical applications including (1) noninvasive assessment of the severity of renal stenosis (hypertension); (2) Quantification of wall-shear stress (WSS) in choriocapillaries (blindness), and (3) Design of alternatives to left ventricle assist device (LVAD) for minimal invasion (Heart transplant).