1. A medical image processing apparatus, comprising: a cardiac cavity region specifying part configured to receive volume data representing a heart and specify a position of a cardiac cavity region represented in the volume data; an axis setting part configured to set an axis intersecting the cardiac cavity region; an image generation plane setting part configured to set an image generation plane including the axis in the volume data; a first image generator configured to, based on the volume data, generate three-dimensional image data that stereoscopically represents a boundary of the cardiac cavity region, which is a boundary of one of regions of the cardiac cavity region divided by the image generation plane; a second image generator configured to, based on data excluding data included in the cardiac cavity region of the volume data, generate two-dimensional image data that two-dimensionally represents a region in the image generation plane; and a display controller configured to generate new synthesized image data by synthesizing the three-dimensional image data and the two-dimensional image data, and cause a display to display a synthesized image based on the new synthesized image data, wherein the cardiac cavity region specifying part is configured to define a mask region about the cardiac cavity region; and the second image generator is configured to generate a two dimensional image using the volume data excluding that of the mask region.