Coronary microvascular dysfunction (CMVD) is closely associated with coronary artery disease; it is an independent risk factor and predicts future coronary events or clinically manifest disease up to 10 years later. To date, non-invasive measurement of CMVD myocardial perfusion heterogeneity imaging (MPHI) by SPECT is not available into clinical practice. We developed a new method to study the CMVD by SPECT. In this study, we use a mathematic technique from entropy analysis to provide precise, objective, automated quantification of MPHI at stress and at rest with SPECT. We sought to assess the prognostic value of MPHI in high-risk diabetic patients being investigated for ischemia. Therefore, we prospectively evaluated the incremental prognostic value of MPHI in patients with type 2 DM during long-term follow-up. Coronary microvascular dysfunction is closely associated with coronary artery disease; it is an independent risk factor and predicts future coronary events or clinically manifest disease up to 10 years later.