The present application describes an apparatus that hinders or even prevents thrombus buildup in the first instance. The apparatus not only occludes the left atrial appendage (LAA), the apparatus eliminates the potential space within the LAA where thrombus formation could form. Numerous examples are described, but principally, an occlusion device is used to block the orifice opening of the LAA, i.e., the ostium, where the occlusion device is configured to allow injection of a biocompatible, inert material into the LAA during implantation. This material is used to fill the LAA acting as a bulking agent. The material may be injected directly into the LAA or in an expandable balloon within the LAA and is maintained in a liquid phase during implantation, which allows the material to better fill the entire LAA volume. In some examples, the occlusion device caps the fluid preventing it from spilling out of the LAA, and thus avoiding the possibility of embolism. In other examples, the fluid levels are monitored during insertion to prevent spillover. Either way, preferably the material is maintained in the liquid phase throughout insertion and then actively converted it into a solid phase by a controllable mechanism, such as application of a catalyst material into the LAA that induces a solid phase in the material or application of an electrical current, radiofrequency energy, heat, light, etc that solidifies the material. In other examples, the transition from liquid phase to solid phase occurs naturally over time, in response to body temperature, or in response to blood entering the LAA. In some examples, the biocompatible, inert material is conductive.