Eustachian valve, also called valvula venae cavae inferior, caval valve, sylvian valve, is an endocardial fold extending from the anterior margin of the inferior vena cava to the anterior part of the limbus fossa ovalis. In embryonic life it helps blood flowing through patent foramen ovale into the left atrium, thus shunting pulmonary circulation. After birth, Eustachian valve becomes an embryogenic remnant. Echocardiography is the standard tool to define correctly this membrane. Moreover, the literature reports some diagnostic pitfalls of this valve, mistaking interpreted as thrombus, vegetation or tumor. Right diagnosis of this membrane is necessary and clinically relevant in the rare cases of infective endocarditis or in the patent foramen ovale because sometimes a redundant valve interferes with Amplatzer PFO occluder placement. In this case report, we describe a prominent Eustachian valve previous interpreted as an endocardiac cyst. Integrated echocardiography (transthoracic, transesophageal and three-dimensional reconstruction) defines correctly diagnosis, anatomy and kinesis of prominent Eustachian valve.