1. A medical image processing device for extracting an endocardium of a left ventricle from 3D image data representing the left ventricle, the device comprising: a blood region extracting unit configured to extract a blood region in the left ventricle from the image data; a convex and concave points identifying unit configured to find a convex hull from a plurality of sample points on a contour of the extracted blood region and identify convex points forming the convex hull and concave points, which are sample points other than the convex points; and an endocardium determining unit configured to deform the contour of the blood region by moving at least a part of the concave points outward from the blood region by an amount determined based on a positional relationship among each concave point and the convex points located around the concave, point and determine a deformed contour of the blood region to be the endocardium.