Introduction: Malignant neoplasms rarely occur in the heart. Tumors metastatic to the heart and pericardium are 20 to 30 times more common than primary lesions, because 10 to 20% of patients with known malignancy have secondary involvement at autopsy. Diagnosis of cardiac tumors has been facilitated by the use of modern imaging, but histologic diagnosis is required, and access to the cardiac tumor is often difficult. Much less frequently, the cardiac metastatic tumor is revealing for an otherwise clinically silent malignancy. We will present the cases of 2 patients consecutively admitted in our clinic, presenting with atrial flutter with a 2:1 atrioventricular conduction in which the arrhythmia revealed a malignancy. Methods: First case – a 60 year old male patient is referred to the clinic for TEE and ablation for a recently diagnosed, 2:1 atrioventricular block, atrial flutter. He denied associated symptoms: shortness of breath, chest pain, pedal edema. Upon admission, the physical examination revealed a regular heartbeat, with a heart rate of 130 bpm. The pulmonary artery was normal, without any significant mass or enlargement. Second case – a 50 year old male patient, smoker, with a history of surgically removed esophageal adenocarcinoma (N0M0) 6 months prior, admitted for 2:1 atrioventricular block atrial flutter. The examination revealed severe resting dyspnea, a heart rate of 150 beats/minute, right side pleural effusion. An ECG confirmed atrial flutter with 2:1 atrioventricular (AV) block. Results: At first case, the evolution was encumbered by the appearance of intense lumbar pain. Unfortunately, the patient rapidly deteriorated, presenting low cardiac output despite drug induced conversion to sinus rhythm and died suddenly, curtailing the diagnostic effort. At the second patient, in the left ventricle, intramyocardial areas with different echogenicity were to be seen, as well as posterior to the left atrium. A thoracic-abdominal-pelvic CT scan was done showing a tumoral mass invading the left atrium and the inferolateral wall of the LV, highly suggestive for a myocardial metastasis. This patient’s condition rapidly worsened as well, dying shortly. Conclusions: We presented the cases of 2 patients consecutively admitted in our clinic, presenting with atrial flutter with a 2:1 atrioventricular conduction in which the arrhythmia revealed a cardiac tumor.