CT myocardial perfusion imaging is an emerging CT application using density measurements of contrast-enhanced left ventricular (LV) myocardium. OBJECTIVE: Using a 320-MDCT we have consistently observed lower Hounsfield unit (HU) values in the lateral LV myocardium, potentially mimicking perfusion defects. This study aimed to evaluate contrast-enhancement patterns of the LV myocardium in normal studies. METHODS: Twenty-one clinical cases with normal coronary MDCT-based angiography findings, as determined by 2 qualified readers, were selected for retrospective evaluation. Using 8 identically sized and positioned ROIs, the HU measurements were recorded from short axis axial reconstructions through the LV myocardium in middle, apical, and basal locations. Scans were acquired on a 320-slice MDCT unit. RESULTS: The middle short axis location demonstrated HU densities of 79.4 (range 42.3-162.7) in the lateral myocardial wall (regions 2, 3, and 4) compared with 103.9 (range 11.4-159.6) in the inferior, septal, and anterior walls (regions 1, 5, 6, 7, and 8; P <0.001). HU densities for the basal slice were 82.3 (range 51.5-168.4) in the lateral wall compared with 94.9 (range 35.3-144) in the inferior, septal, and anterior walls (P <0.001). In the apical location, HU densities were 79.9 (range 42.3-139.3) in the lateral wall compared with 100.9 (range 69.0-170.5) in the inferior, septal, and anterior walls (P <0.001). CONCLUSION: Normal LV myocardial enhancement using a 320-slice MDCT demonstrates significantly lower densities in the lateral wall when compared with the anterior, septal, and inferior walls in patients with normal coronary vascular anatomy. Assessment of CT myocardial perfusion studies should therefore be undertaken with caution, to prevent misrepresenting these lower-density values in the LV lateral wall.