We report a clinical case of a 64-year-old male with known apical hypertrophic cardiomyopathy, who presented to the hospital with new-onset persistent atrial fibrillation. An electrical cardioversion (ECV) was planned after one month of anticoagulation therapy and transesophageal echocardiogram (TEE) was performed beforehand. During the TEE thrombus in the left atrial appendage was detected, as well as a heterogeneous, hyperechoic, vascularized and non-mobile structure in the left atrium (LA). The ECV was cancelled and the patient was sent for computerized tomography (CT) chest scan. It revealed a big mass in the right lung with macromorphology of central lung carcinoma. There was tumor infiltration of the pericardium and the LA, as well as adrenal and liver metastases. The patient was sent for bronchoscopy with biopsy.