1. An image processing apparatus comprising: a storage unit configured to store data of a first image including a contrast-enhanced cardiac region; a first specification unit configured to specify a specific region included in the cardiac region on the basis of a distribution of pixel values of the data of the first image; a setting unit configured to contract the specified specific region, and set an ROI to the contracted specific region; and a calculation unit configured to calculate an index concerning the set ROI, the index being associated with a function of the specific region.