Heart tumors are often underestimated by professionals in the field. Being relatively rare, secondary neoplasms are mostly the result of advanced malignant melanoma, lymphoma, and leukemia. Benign tumors such as myxomas, lipomas, papillary fibroelastomas, angiomas, and fibromas represent about 75% of primary cardiac tumors [
1,
2]. A separate non-neoplastic benign cardiac lesion, that may be mistaken for various heart tumors, is lipomatous hypertrophy of the atrial septum (LHAS), first described by Prior in 1964, based on autopsy study [
3]. The etiology of LHAS has not been recognized. It is presumed that due to the involvement of embryonic mesenchymal cells in the primary formation of atria, the atrial septum cells may differentiate into adipocytes with appropriate stimuli [
4]. In the histological image analysys, no mitoses are observed, hence the change does not represent a malignancy [
5]. Morphologically, it is presented as a non-encapsulated excessive epicardial fat deposition in the septum secundum, that infiltrates the area of the interatrial septum that spares the fossa ovalis [
6]. The thickness of the septum can reach 20 mm and more [
7]. Accumulation of adipose tissue can also be observed in subepicardium, crista terminalis, endocardium, and mediastinum. In differential diagnostics, it is required to take into account possible adipose tissue neoplasms. Unlike LHAS, lipomas are encapsulated, round, homogeneous and do not infiltrate myocardium fibers. Lipomatous hypertrophy is associated with obesity and is seen more frequently in elderly and female patients [
8,
9]. Development of imaging techniques has enabled more frequent recognition of usual asymptomatic masses [
10]. In a prospective study using computed tomography, lipomatous hypertrophy was identified in 2.2% of the patients [
11]. Extremely rare infiltration of adipocytes, causing distortion of the septum, may pose life-threatening cardiovascular complications requiring urgent cardiac surgery intervention [
12]. The rare complications of LHAS include superior vena cava syndrome, severe cardiac arrhythmias (sick sinus syndrome, arrhythmias, changes in P waveform morphology in ECG), pericardial effusion, heart failure and sudden cardiac death [
13,
14]. However, the majority of cases are clinically silent and are detected accidentally during routine chest X-ray, echocardiography, surgery or autopsy [
15].