Background: Although the calculation of myocardial extracellular volume (ECV) with T1 mapping MRI sequences has not been demostrated to be useful in conditions with focal myocardial fibrosis such as ischemic or hypertrophic myocardiopathies, it has been proven to be reliable for the detection of diffuse myocardial fibrosis in other types of myocardiopathies. However the method is time consuming and this my hinder its applicbility in daily clinical practice. In our experience, the inter and intra-observer variability in the calculation of segmental myocardial ECV is least in segments 9 (inferoseptal-basal) and 3 (middle). Purpose: To analyze the usefulness of segmental ECV measurement as a surrogate of global ECV in order to simplify and expedite myocardial ECV calculation with T1 mapping MRI. Methods: We evaluated 265 patients; 47 of them were normal (N group), 120 had diffuse pathology (D group) and 100 had diffuse pathology (F group). A 1.5T system MRI study (Siemens Avanto) was conducted in each patient, including T1 sequences before and 15 minute after administration of gadolinium (Gd) following a Sh-MOLLI protocol with three ventricular cuts in the sort-axis plane. The global ECV calculation was carried out with the 16 segments visualized. Results: Pearson`s linear correlation was best in the inferoseptal 3 (r 0.85) and 9 (r 0.864) segments and worst in the inferolateral 5 (r 0.708) and 15 (r 0.733) segments. (p.000 in all cases). Compared with global ECV, the ECV-3 was significantly lower (0.289 vs 0.2898; p .000), while the ECV-9 presented similar results (0.2902 vs 0.2892; p 0.816). In the N group, values of ECV-9 and global ECV were identical (0.2682 vs 0.2682; p 0.989), and there were no significant differences in the D group (0.2847 vs 0.2841; p 0.784) nor in the F group (0.3066 vs 0.3055; p 0.793). ECV-9 had the highest correlation coefficient in both diseased groups (D: r 0.941; F: r 0.817). Conclusion: Segmental calculation of ECV as marker of diffuse interstitial fibrosis through T1 mapping sequences and the Sh-MOLLI protocol is useful and reliable method. Tne analysis of the inferoseptal-middle (9) segment is the most representative and present the lowest variability.