Another Patient

Introduction
Invasive hemodynamic and angiographic study is not necessary in our patient, because all manifestations of this condition have been accurately defined by the history and physical examination and echocardiography. An angiogram from another patient is shown for your edification.

Another patient's cath
This is a systolic still-frame of the left ventriculogram in the right anterior (RAO) oblique view from another patient. Note the structure identified by the arrow.
Choose the best description of the structure identified by the arrow in the left ventriculogram.