The volume of myocardial tissue that is perfused by an epicardial coronary artery has been shown to be predictably related to the epicardial arterial lumen diameter. However, to what extent the intra-myocardial microvasculature follows the epicardial rules remains uncertain. To explore the relationship between the diameter of coronary arterioles and their subsequent perfused myocardial volumes, we quantified the volume of non-perfused myocardium resulting from an embolized arteriole of a certain diameter. We injected a single dose of microspheres, selected from one of the nine possible combinations of microspheres (10, 30 or 100 µm diameter, each one at three possible doses) into the LAD and/or LCX of seven anesthetized pigs. At postmortem, the coronary arteries were infused with a radiopaque silicon polymer. One cm³ of embolized myocardium was scanned with a micro-CT scanner resulting in 3-D images consisting of 20 µm and a sub-volume of the specimen with 4 µm cubic voxels. Image analysis provided the number and the volumes of myocardial perfusion defects for each size and dose of microspheres. The smallest individual myocardial perfusion defect, corresponding to the volume of myocardium perfused by a single embolized arteriole, was found to be 0.0004 ± 0.0002, 0.02 ± 0.004 and 0.62 ± 0.099 mm³ for the 10, 30 and 100 µm microspheres, respectively. The number of myocardial perfusion defects in the embolized myocardium was inversely related to the dose of the injected microspheres, reflecting a clustering behavior, consistent with a random distribution process of the individual embolized perfusion defects.