Late Gadolinium Enhancement (LGE) pattern of cardiac amyloidosis (CA) at cardiac magnetic resonance (CMR) examination is absent in approximately 30% of patients. We tested whether the evaluation of myocardial gadolinium signal intensity (SI) decay (SID) has a higher diagnostic accuracy for CA. CMR was performed in 59 patients with systemic AL amyloidosis (36 males, 69 ± 10 years, mean ± SD), and 20 age/sex-matched healthy controls. LGE images were acquired every minute up to 8 min after gadolinium injection (time of inversion 250 ms). SI regions of interest were plotted in SI/time curves for endocardial (Endo) and epicardial layer of interventricular septum, cavity, and skeletal muscle as reference. SID (a negative exponential function described by the parameter TSID) was expressed as number of heart beats (HB) from each ROI. The typical LGE pattern for CA was detected in 42 patients (Ty-LGE), while 17 showed either absent LGE or an atypical pattern (ATy-LGE). A definite CA diagnosis was confirmed in all Ty-LGE patients and in 10/17 ATy-LGE patients. At ROC analysis Endo-TSID was the most accurate parameter to distinguish Ty-LGE and ATy-LGE patients from controls. A 269 HB threshold (mean + 2 SD Endo-TSID measured in controls) identified 51/52 patients with definite CA diagnosis, with 98% sensitivity, 93% specificity, and 96% diagnostic accuracy. A direct relation was found between the extracellular volume and Endo-TSID in CA patients (r 0.72, 95% CI 0.37-089, p < 0.001). the analysis of myocardial SID after gadolinium injection improves the accuracy of CMR for CA diagnosis.