1. A medical image processing apparatus, comprising: a storage device, including a medical image data obtaining unit and a region extraction processing unit; and a hardware processor, coupled to the storage device; wherein the hardware processor activates the medical image data obtaining unit for obtaining medical image data containing an image of a heart; and the hardware processor activates the region extraction processing unit for initially only extracting a left ventricular region that combined a contrast region and a myocardial region surrounding the contrast region of the left ventricular region of the heart among the left ventricular region, a right ventricular region, a left atrium, and a right atrium region of the heart contained in the medical image data based on the medical image data obtained by the medical image data obtaining unit by using a graph cut method, wherein processing target pixels that combined an initial region of the left ventricular region and an area surrounding the initial region are determined by using a plurality of landmarks, wherein after the left ventricular region of the heart had been extracted and before the right ventricular region is initially extracted, the region extraction processing unit sets an evaluation function that assigns higher costs with respect to pixels within the left ventricular region of the heart, and performs a region extraction process to extract at least one of the right ventricular region, the left atrium region, and the right atrium region of the heart by the graph cut method, wherein the medical image data obtaining unit obtains a plurality of medical image data in different phases of one cardiac cycle of the heart which is beating, the region extraction processing unit extracts a left ventricular region in medical image data of one medical image in diastole of the plurality of medical image data, then extracts, based on the extraction result of the left ventricular region, at least one of a right ventricular region, a left atrium region, and a right atrium region in the medical image data of one medical image in diastole, and extracts, based on the extraction result of the medical image data of one medical image in diastole, at least one of a right ventricular region, a left atrium region, and a right atrium region in medical image data in a phase other than that of the medical image data of one medical image in diastole, and the region extraction processing unit extracts a left ventricular region in medical image data of one medical image in end-diastole of the plurality of medical image data, then extracts, based on the extraction result of the left ventricular region, at least one of the right ventricular region, the left atrium region, and the right atrium region in the medical image data of one medical image in end-diastole, and extracts, based on the extraction result of the medical image data of one medical image in end-diastole, at least one of the right ventricular region, the left atrium region, and the right atrium region in medical image data in the phase other than that of the medical image data of one medical image in end-diastole.