Cardiac amyloidosis is a disease characterized by the deposition of amyloid material in the extracellular matrix of the myocardium.Arrhythmias are part of the broad spectrum of the disease, with atrial fibrillation (AF) being the most common.Due to the heterogeneity of cardiac amyloidosis, its real incidence is unknown, denoting an underdiagnosis and in many cases being hidden under the presentation of a common heart disease, which leads to silent progression and worse outcomes.We describe the clinical case of a patient with AF refractory to electrical cardioversion and ablation therapy in the context of cardiac transthyretin amyloidosis (ATTR), initially unnoticed and found as an incidental diagnosis.The purpose of this report is to review the association between AF and ATTR, its epidemiology, pathophysiology, signs and symptoms, diagnosis and treatment in order to provide medical staff with tools for a timely diagnosis of a poorly recognized disease.