The medical image diagnostic device of the present invention is a medical image diagnostic device provided with a tomography image construction unit for constructing a tomography image of a subject body, a measurement unit for measuring cardiac measurement values on the basis of the tomography image； and an image display unit for displaying the tomography image and the cardiac measurement values； wherein the medical image diagnostic device is provided with a characteristic waveform detection unit for detecting a characteristic waveform from the shape of the ECG waveform of the subject body； and a cardiac period setting unit which treats as a first characteristic waveform a characteristic waveform which, among characteristic waveforms detected at the characteristic waveform detection unit, has the smallest difference in time relative to a reference time, and sets a cardiac period, which is set according to a second characteristic waveform succeeding the first characteristic waveform, and the first characteristic waveform； wherein the measurement unit measures the cardiac measurement values on the basis of the tomography image, the characteristic waveform, and the cardiac period.
