AIMS: Combined magnetic resonance imaging (MRI) of molecular and morpho-functional changes might prove highly valuable for the elucidation of pathological processes involved in the development of cardiac diseases. Our aim was to test a novel MRI reporter gene for in vivo assessment of the canonical Wnt/beta-catenin/TCF pathway activation, an important regulator of post-ischemic cardiac remodeling. METHODS AND RESULTS: We designed and developed a chimeric construct encoding for both of iron-binding human ferritin heavy chain (hFTH) controlled by the beta-catenin-responsive TCF/Lef promoter and constitutively expressed green fluorescent protein (GFP). It was carried by adeno-associated virus serotype 9 (rAAV9) vectors and delivered to the peri-infarct myocardium of rats subjected to coronary ligation (n=11). By 1.5-Tesla MRI and a multiecho T2* gradient echo sequence, we detected iron accumulation only in the border zone of the transduced infarcted hearts. In the same cardiac area, postmortem histological analysis confirmed the co-existence of iron accumulation and GFP. The iron signal was absent when rats (n=6) were chronically treated with SEN195 (10 mg/kg/day), a small-molecular inhibitor of beta-catenin/TCF-dependent gene transcription. Canonical Wnt pathway inhibition attenuated the post-ischemic remodeling process, as demonstrated by the significant preservation of cardiac function, the 42+/-1% increase of peri-infarct arteriolar density and 43+/-3% reduction in infarct scar size compared with untreated animals. CONCLUSIONS: The TCF/Lef promoter-hFTH construct is a novel and reliable MRI reporter gene for in vivo detection of the canonical Wnt/beta-catenin/TCF activation state in response to cardiac injury and therapeutic interventions.