Cardiac CT myocardial perfusion is an emerging tool utilizing differences in myocardial density of ischemic compared to normal myocardium. We sought to document the contrast enhanced density profile of myocardial segments subtended by severely stenotic coronary arteries on rest (non stress) cardiac CT imaging, and compare the density with identical segments without ischemic disease. 100 cardiac CT studies were identified resulting in 25 normal patients, 37 with severe left anterior descending artery stenosis, 14 with severe left circumflex artery stenosis, and 24 with severe right coronary artery stenosis. The studies were reviewed on a workstation with dedicated myocardial analysis software. Left anterior descending artery ischemic segments (apical anterior and apical septal) measured 82.2 (?3) and 102 (?3) Hounsfield unit (HU) respectively comparing with non-ischemic segments 89 (?4) and 109 (?4) HU respectively (both P values 0.16). Left circumflex artery segments (basal anterolateral and mid anterolateral) demonstrated 80 (?4) and 76 (?4) HU respectively compared to non-ischemic segments, 89 (?4) and 87 (?4) HU (P value 0.13 and 0.07 respectively). Right coronary artery ischemic segments (basal inferoseptal and basal inferior) measured 104 (?3) and 105 (?3) HU respectively and these compared with non-ischemic segments, 102 (?4) and 105 (?4) HU respectively (P Value 0.69 and 0.94 respectively). Comparison of ischemic myocardial segments with non-ischemic segments demonstrated no significant difference in myocardial density. In prospectively acquired resting 320 multi detector CT, the myocardium subtended by severely stenotic vessels demonstrates no significant density difference compared with those supplied by vessels with no stenosis, confirming that myocardial ischaemia cannot be reliably detected on rest coronary computed tomography angiography by qualitative nor quantitative assessment.