Objectives To investigate whether cardiovascular magnetic resonance (CMR) T(1)mapping and strain parameters can detect early histological and functional myocardial changes in idiopathic inflammatory myopathy (IIM) with negative late gadolinium enhancement (LGE) and preserved ejection fraction. Methods Thirty consecutive patients with IIM (41.5 +/- 15.4 years, 24 females) who did not have LGE or reduced left ventricular ejection fraction (LVEF) and 30 age- and gender-matched healthy controls (40.6 +/- 14.2 years, 20 females) were recruited. Patients with IIM were further classified into two subgroups according to high-sensitivity cardiac troponin I (hs-cTnI) values: elevated hs-cTnI subgroup (n= 10) and normal hs-cTnI subgroup (n= 20). Myocardial native T(1)values, extracellular volume (ECV) fractions, and strain parameters were analyzed in patients with IIM and healthy controls. Results Compared with healthy controls, patients with IIM had significantly prolonged native T(1)values and increased ECV in each LV segment (p< 0.05). In further subgroup analysis, LV mid-slice native T(1)values had the most power to discriminate between patients with elevated hs-cTnI and healthy controls (area under the curve = 0.92). There was no significant difference of global LV strain or strain rates between IIM patients and controls. Conclusions Diffuse interstitial fibrosis can be detected by CMR T(1)mapping in patients with IIM who do not have LGE or reduced LVEF or elevated hs-cTnI, and it may be a promising method for screening subclinical cardiac involvement in IIM.