Ischemic mitral regurgitation (iMR) augments risk for right ventricular dysfunction (RV_DYS). Right and left ventricular (LV) function are linked via common coronary perfusion, but data is lacking regarding impact of LV ischemia and infarct transmurality—as well as altered preload and afterload—on RV performance. In this prospective multimodality imaging study, stress CMR and 3-dimensional echo (3D-echo) were performed concomitantly in patients with iMR. CMR provided a reference for RV_DYS (RVEF < 50%), as well as LV function/remodeling, ischemia and infarction. Echo was used to test multiple RV performance indices, including linear (TAPSE, S′), strain (GLS), and volumetric (3D-echo) approaches. 90 iMR patients were studied; 32% had RV_DYS. RV_DYS patients had greater iMR, lower LVEF, larger global ischemic burden and inferior infarct size (all p < 0.05). Regarding injury pattern, RV_DYS was associated with LV inferior ischemia and infarction (both p < 0.05); 80% of affected patients had substantial viable myocardium (< 50% infarct thickness) in ischemic inferior segments. Regarding RV function, CMR RVEF similarly correlated with 3D-echo and GLS (r = 0.81–0.87): GLS yielded high overall performance for CMR-evidenced RV_DYS (AUC: 0.94), nearly equivalent to that of 3D-echo (AUC: 0.95). In multivariable regression, GLS was independently associated with RV volumetric dilation on CMR (OR − 0.90 [CI − 1.19 to − 0.61], p < 0.001) and 3D echo (OR − 0.43 [CI − 0.84 to − 0.02], p = 0.04). Among patients with iMR, RV_DYS is associated with potentially reversible processes, including LV inferior ischemic but predominantly viable myocardium and strongly impacted by volumetric loading conditions.