MRI is a valuable tool for diagnosing heart disease today. The cardiac blood flow is determined by an MRI image analysis and expert system. Image data are taken by a TV camera and digitalized. After gray level thresholding and region segmentation, the boundary of the regurgitant flow region is precisely extracted. Using this expert system, a doctor can easily make an accurate diagnosis of the valvular heart disease. This method should prove useful for the diagnosis of various heart diseases.