Two-dimensional echocardiography is the technique of choice for identifying cardiac masses. Unfortunately, adjacent structures compressing the atrial wall may lead to misdiagnosis. Clinicians should promptly recognize this phenomenon and the related diagnostic features. The case of a 90-year-old woman presenting with a history of recent onset effort dyspnea is described. On transthoracic two-dimensional echocardiography a left atrial mass which closely mimicked an atrial myxoma was evident. A tomographic scan revealed a large sliding hiatus hernia, which was confirmed on traditional radiographic examination. The echocardiographic characteristics of the mass are described in detail, as well as a review of the literature for the purpose of a correct differential diagnosis.