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Objective Myocardial fibrosis is a potential mechanism of light-chain myocardial amyloidosis(AL-CA). This research aimed at exploring the correlation between multiparameter cardiac magnetic resonance (CMR) and myocardial fibrosis by relating the CMR myocardial tissue characteristics, the morphological and the functional parameters with gallium-68-labeledfibroblast activation protein inhibitor 04 positron emission tomography (68Ga-FAPI PET). Methods We gave the patients diagnosed with AL-CA in Peking Union Medical College Hospital from August to December 2021 the examinations of CMR and 68Ga-FAPI PET/CT. We recorded and analyzed the information on clinical manifestations and examinations of the patients. Results A total of 23 patients with AL-CA were included, 15 (65.2%)of which were male and the mean age was 58.3±6.5 years. Patients with high 68Ga-FAPI-04 uptake had shown growth in myocardial extracellular volume (ECV), significantly higher than those in the negative group (P=0.047). In addition, patients' myocardial ECV was positively correlated with myocardial FAPI uptake (r=0.628, P=0.001;r=0.727, P < 0.001;r=0.661, P=0.001). Patients in the positive group showd reduced left ventricular (LV) ejection fraction (EF)(P < 0.001).LVEF (r=-0.798, P < 0.001;r=-0.794, P < 0.001; r=-0.795, P < 0.001) and right ventricular (RV)EF (r=-0.735, P < 0.001;r=-0.739, P < 0.001;r=- 0.684, P < 0.001) showd negatively correlated with myocardial FAPI uptake, LV circumferential strain (r=0.668, P < 0.001;r=0.708, P < 0.001;r=0.705, P < 0.001), LV longitudinal strain (r=0.629, P=0.001;r=0.635, P=0.001; r=0.597, P=0.003), and RV longitudinal strain (r=0.575, P=0.004; r=0.792, P < 0.001;r=0.673, P < 0.001) were negatively correlated with myocardial FAPI uptake. Conclusions FAPI-related fibroblast activation is concurrent with CMR-related abnormal myocardial interstitial characteristics that leads to the decreased function of the myocardial movement. Patients with increased FAPI uptake present with increased ECV, decreased EF, and decreased strain with morphological abnormalities.