Summary: This paper describes a clinically translatable interventional guidance platform to improve the accuracy and precision of stem cell injections into a beating heart. The proposed platform overlays live position of an injection catheter onto a fusion of a pre-procedural MR roadmap with real-time 3D transesophageal echocardiography (TEE). Electromagnetic (EM) tracking is used to initialize the fusion. The fusion is intra-operatively compensated for respiratory motion using a novel algorithm that uses peri-operative full volume ultrasound images. Validation of the system on a moving heart phantom produced a landmark registration accuracy of $2.8 \pm 1.45 \,\text{mm}$. Validation on animal in vivo data produced an average registration accuracy of $2.2 \pm 1.8 \,\text{mm}$; indicating that it is feasible to reliably and robustly fuse the MR road-map with catheter position using 3D ultrasound in a clinical setting.