Atrial fibrillation induced stroke accounts for up to 15% of all strokes. These strokes are caused approximately 90% of the time by clot formation in the left atrial appendage (LAA). To prevent these clots, the most common approach is to administer blood thinners. However, contraindications prevent some people from being able to have blood thinners. Devices have been developed to seal the LAA to prevent clot formation in these patients. Current devices, such as the LARIAT® tie off the LAA theoretically preventing blood from entering the LAA. These have had limited clinical success mainly due to failure to completely close the LAA leaving holes and orifices for thrombi to form. To overcome this lack of complete closure, many surgeons use off-label approaches, classically filling the LAA filamentous coils, to cover these holes. Although this usually helps largely cover the holes, placement is challenging, the coils can migrate, the holes are not fully closed as there is space within and around the coils that don't fully mold to the LAA geometry. Furthermore, the coils can develop device related thrombi defeating their purpose. Therefore, these are not fully sufficient to complement the closure techniques in closing the LAA. To address limitation of the closure devices and coil sealing of remaining holes, we developed a thermally responsive hydrogel (Thermogel) that solidifies once injected into the LAA to uniformly and fully close off the LAA thus preventing clot formation and device related thrombi. This Thermogel consists of three portions: 1) a structural component composed of thiolated Pluronic F127 for gel to solid transition following injection, 2) Heparin for anticoagulation, and 3) Dopamine for adhesion to the surrounding endothelium in the turbulent flow encountered in cardiovascular applications. Here we have demonstrated that Thermogel, in conjunction with the LARIAT®, is capable of filling the defects in small and large animals through catheter injection. Thermogel was biocompatible and led to atrophy of the LAA at 5 weeks in a large animal model. Given the advantages of this Thermogel for sealing this defect and ability to be delivered through an endovascular approach, Thermogel presents a viable adjuvant to current occlusion-based treatments for sealing cardiovascular defects.