ABSTRACT The Embryonic Stem Cell Growth and Genetically Modified Models Core (Core B) will provide service to all four Projects with the goal of efficiently generating and providing cellular and animal experimental models of congenital heart disease (CHD) to Program participants. Aim 1 will provide human and mouse embryonic stem cell (hESC and mESC)-derived cellular models of CHD to the projects. This will include (1a) providing support for genome editing of hESC and mESCs, (1b) maintaining high quality stocks of existing and newly generated hESC and mESC lines used by each project, and (1c) providing assistance with hESC and mESC differentiation towards cardiac lineages. Aim 2 will provide mouse genetic models of CHD to the projects. This will include (2a) providing support for the generation of new genetically modified mouse models, (2b) establishing and maintaining breeding stocks for new and existing mouse models to be used by the Projects, and (2c) providing experimental animals for each Project. Core B personnel are well-trained in all aspects of the cellular and animal services to be provided. The goal of the Core is to provide centralized, quality-controlled reagents to the Projects, thereby maximizing efficiency and minimizing the costs associated with the usage of cellular and animal models. Given the heavy reliance on genetically modified models (both cellular and animal) and the proven performance of the Core personnel, the importance of Core B to the success of this Program Project Grant application cannot be overstated.