Atrial myxomas are the most common cardiac tumor in adults (FA2020 p316).

Myxomas can cause "ball-valve" obstruction in the left atrium associated with syncopal episodes. Myxoma is a myxoid tumor of primative connective tissue and is composed of myxoma cells in a gelatinous glycosaminoglycan matrix. Thus, the description of a heterogenous pedunculated mass would fit.

Aarterial emboli can associated with myxomas, though none occurred in this patient.