Lipomatous lesions of the heart involving the atria and interatrial septum are not well known. Most such lesions do not become clinically significant; however, intractable arrhythmias, blood flow obstruction, and valvular disruption may result from extensive fatty infiltration of the atrial wall or from the mass effect of benign or malignant lipomatous tumors. Some fatty lesions may be difficult to characterize radiologically, and misdiagnosis may lead to unnecessary surgical interventions. We describe the pathology of the most common fatty lesions and underscore some of the radiographic and surgical issues pertaining to the diagnosis and management of these masses.