Left ventricular (LV) myocardial contrast enhancement can be recorded using 320 multi detector computed tomography (MDCT). We aimed to (1) assess patterns of regional myocardial perfusion at rest and compare them with NH3 positron emission tomography (PET) (2) and to assess the effect of intravenous adenosine infusion on regional myocardial perfusion. To evaluate myocardial perfusion patterns at rest, we scanned 14 healthy subjects with PET and 14 age and gender matched subjects with 320 MDCT. To evaluate the effect of adenosine stress on relative perfusion patterns 14 subjects with nearnormal epicardial coronary arteries were studied at rest and during adenosine stress. Relative perfusion was assessed as attenuation density (AD) in 16 segments of the LV, and each segment was divided into 3 layers: endo-, mid- and epi-cardial. During rest the relative AD byMDCT was lower in the lateral wall compared with the remainder of theLV (P\0.002).A similar pattern was found by PET-imaging. LV endocardial AD was higher than mid- and epicardial AD (P\0.05). At rest the endocardial/epicardial ratio in the septum was 0.99 compared with 1.23 in nonseptal segments (P\0.001). During adenosine infusion transmural AD increased due to significant increases in the mid- and epicardium and the endocardial/ epicardial ratio decreased by 18% in non-septal segments (from 1.23 to 1.05 P\0.001). Relative perfusion at rest is lower in the lateral wall of the LV with both PET and MDCT compared to the remainder of the myocardium. During adenosine stress endocardial/ epicardial ratio decrease significantly.