A system for determining the presence or absence of myocardial ischemia in a subject, by analyzing medical images of at least one region of the heart of a subject of interest during a first-pass dose of a contrast agent or tracer, the plurality of medical images being acquired in a consecutive manner by a medical imaging modality, the system comprising (i) a delineation unit, configured to delineate contours of a selected region of the heart of the subject of interest in the plurality of medical images and to divide the selected region into a plurality of myocardial layers; and (ii) an intensity sampler and analyzing unit configured to: sample signal intensities of myocardial image positions from the plurality of medical images, and, for each of the myocardial layers and a reference point in the heart, analyse a sampled signal intensity in the selected region over time and compare the time taken to reach peak intensity of the signal intensities of the myocardial layers with the time taken to reach peak intensity of the signal intensity of the reference point in the heart to determine a first index number indicative of a spatio-temporal perfusion inhomogeneity or perfusion dephasing among at least a subset of the myocardial layers in the said region; compare the first index to a first comparative index number obtained in a normal heart; and where said first index number is greater, diagnosing the presence of ischemia, wherein: the delineation unit is further arranged to segment at least a selected part of the heart of the subject of interest in the plurality of medical images into a plurality of radial myocardial segments; the intensity sampler and analyzing unit is further configured to sample and analyse the medical images obtained over time and, for each of the plurality of radial myocardial segments, analyse a sampled signal intensity over time and compare the results with those obtained at a reference point in the heart to determine a second index number indicative of a spatio-temporal perfusion inhomogeneity or perfusion dephasing among at least a subset of radial myocardial segments of the plurality of radial myocardial segments, compare the second index number to a second comparative index number obtained in a normal or model heart, and where said second index number is greater, recording a positive result; and when the presence of ischemia is diagnosed using the first index number, then the second index number is used to distinguish microvascular dysfunction, MVD, from coronary artery disease, CAD, in the subject of interest. (i) a delineation unit, configured to delineate contours of a selected region of the heart of the subject of interest in the plurality of medical images and to divide the selected region into a plurality of myocardial layers; and (ii) an intensity sampler and analyzing unit configured to: sample signal intensities of myocardial image positions from the plurality of medical images, and, for each of the myocardial layers and a reference point in the heart, analyse a sampled signal intensity in the selected region over time and compare the time taken to reach peak intensity of the signal intensities of the myocardial layers with the time taken to reach peak intensity of the signal intensity of the reference point in the heart to determine a first index number indicative of a spatio-temporal perfusion inhomogeneity or perfusion dephasing among at least a subset of the myocardial layers in the said region; compare the first index to a first comparative index number obtained in a normal heart; and where said first index number is greater, diagnosing the presence of ischemia, the delineation unit is further arranged to segment at least a selected part of the heart of the subject of interest in the plurality of medical images into a plurality of radial myocardial segments; the intensity sampler and analyzing unit is further configured to sample and analyse the medical images obtained over time and, for each of the plurality of radial myocardial segments, analyse a sampled signal intensity over time and compare the results with those obtained at a reference point in the heart to determine a second index number indicative of a spatio-temporal perfusion inhomogeneity or perfusion dephasing among at least a subset of radial myocardial segments of the plurality of radial myocardial segments, compare the second index number to a second comparative index number obtained in a normal or model heart, and where said second index number is greater, recording a positive result; and when the presence of ischemia is diagnosed using the first index number, then the second index number is used to distinguish microvascular dysfunction, MVD, from coronary artery disease, CAD, in the subject of interest.