If E is an elliptic curve over Q and K is an imaginary quadratic field, there is an Iwasawa main conjecture predicting the behavior of the Selmer group of E over the anticyclotomic Z_p-extension of K. The main conjecture takes different forms depending on the sign of the functional equation of L(E/K,s). In the present work we combine ideas of Bertolini and Darmon with those of Mazur and Rubin to shown that the main conjecture, regardless of the sign of the functional equation, can be reduced to proving the nonvanishing of sufficiently many p-adic L-functions attached to a family of congruent modular forms.