The mass splittings of the pseudoscalar and vector D and B light-heavy quark systems are being calculated using the method of QCD sum rules. Electromagnetic, quark mass, and nonperturbative QCD effects are all included. In this progress reprot we demonstrate that nonperturbative isospin violating effects are small and emphasize the need for an accurate gauge invariant calculation of electromagnetic effects, which would allow the isospin splittings for heavy-light masons to give valuable information about quark mass splittings.