Unusual case of prominent Chiari network trapped in the left atrium

We describe a case of an unusually prominent Chiari network in a premature neonate who was evaluated with echocardiography. The network, which is an embryologic remnant, was extensive, mobile, and moved in and out of the right ventricle. Later, tissue strands passed the foramen ovale and ultimately became trapped in the left atrium. The differential diagnosis included thrombus, tumor, vegetation, and ruptured chordae.