  We study the variation of Iwasawa invariants of the anticyclotomic Selmer
groups of congruent modular forms under the Heegner hypothesis. In particular,
we show that even if the Selmer groups we study may have positive coranks, the
mu-invariant vanishes for one modular form if and only if it vanishes for the
other, and that their lambda-invariants are related by an explicit formula.
This generalizes results of Greenberg-Vatsal for the cyclotomic extension, as
well as results of Pollack-Weston and Castella-Kim-Longo for the anticyclotomic
extension when the Selmer groups in question are cotorsion.
