The aim of the present study was to prospectively compare contrast-enhanced magnetic resonance imaging (CE-MRI) with single-photon emission tomography using (201)Thallium chloride (SPECT Tl) in the detection of myocardial viability. Patients with chronic coronary artery disease and systolic dysfunction defined by an ejection fraction (EF) <or= 45% were included. CE-MRI was performed 10-15 minutes after the administration of a gadolinium-based contrast agent using an Inversion Recovery Turbo FLASH (fast low-angle shot) sequence. A 4-hour rest redistribution protocol was used for SPECT Tl. Radionuclide ventriculography was used for the assessment of EF. Forty patients with an EF of 33.1 +/- 7.7% were included. Thirty-two underwent a follow-up examination after revascularization. Comparison of viability assessment was performed in 1360 segments. Agreement was noted in 1065 (78.3%) segments, resulting in a kappa value of 0.336. Discrepancies were observed in 96 SPECT Tl viable segments that were described as nonviable according to CE-MRI and in 199 SPECT Tl nonviable segments that were viable in the CE-MRI study. In patients undergoing the follow-up examination, EF increased by 5.5 +/- 7.3% (33.6 +/- 8.6% to 39.2 +/- 9.7%), but the relation between the amount of dysfunctional viable myocardium defined by both methods studied and the change in EF after revascularization was very weak and not statistically significant. Moderate agreement in the myocardial viability assessment between CE-MRI and SPECT Tl was observed. CE-MRI seems to be more accurate in identifying myocardial viability in inferior and inferolateral segments. We were unable to verify if either of the methods studied is useful for the prediction of EF improvement after revascularization.