The objectives of this study were to define the relationship between the first order constant of Gd-DTPA transfer (K1) and the myocardial blood flow (MBF) at rest and to compare it with an equivalent relationship obtained for positron emission tomography (PET). In a canine model of permanent coronary occlusion (n = 4), myocardial and blood time concentration curves obtained by ¹³N-ammonia PET and Gd-DTPA-enhanced MRI were fitted by a one-compartment model to determine K1. A linear relationship was observed between MRIderived K1 and MBF measured by microspheres (K1 = 0.88 × flow −0.015, R = 0.95), which compares favorably with the equivalent relationship derived from PET (K1 = 0.74 × flow +0.16, R = 0.88). The results of this preliminary study suggest that, at rest and distal to a permanently occluded coronary artery, myocardial perfusion quantification by MRI is possible and can challenge PET.