Simultaneous dual-isotope SPECT imaging with 201Tl and ¹²³I-β-methyl-p-iodophenylpentadecanoic acid (BMIPP) is used to study the perfusion–metabolism mismatch. It predicts post-ischemic functional recovery by detecting stunned myocardium. On the other hand, ^99mTc-MIBI is another radioisotope widely used in myocardial perfusion imaging because of its better image quality and lower radiation exposure than 201Tl. However, since the photopeak energies of ^99mTc and ¹²³I are very similar, crosstalk hampers the simultaneous use of these two radioisotopes. To overcome this problem, we conducted simultaneous dual-isotope imaging study using the D-SPECT scanner (Spectrum-Dynamics, Israel) which has a novel detector design and excellent energy resolution. We first conducted a basic experiment using cardiac phantom to simulate the condition of normal perfusion and impaired fatty acid metabolism. Subsequently, we prospectively recruited 30 consecutive patients who underwent successful percutaneous coronary intervention for acute myocardial infarction, and performed ^99mTc-MIBI/¹²³I-BMIPP dual-isotope imaging within 5 days after reperfusion. Images were interpreted by two experienced cardiovascular radiologists to identify the infarcted and stunned areas based on the coronary artery territories. As a result, cardiac phantom experiment revealed no significant crosstalk between ^99mTc and ¹²³I. In the subsequent clinical study, ^99mTc-MIBI/¹²³I-BMIPP dual-isotope imaging in all participant yielded excellent image quality and detected infarcted and stunned areas correctly when compared with coronary angiographic findings. Furthermore, we were able to reduce radiation exposure to significantly approximately one-eighth. In conclusion, we successfully demonstrated the practical application of simultaneous assessment of myocardial perfusion and fatty acid metabolism by ^99mTc-MIBI and ¹²³I-BMIPP using a D-SPECT cardiac scanner. Compared with conventional ²⁰¹TlCl/¹²³I-BMIPP dual-isotope imaging, the use of ^99mTc-MIBI instead of ²⁰¹TlCl improves image quality as well as lowers radiation exposure.