The purpose of this study is to learn more about the investigational drug, ION-682884 which may be helpful in treating Transthyretin-Mediated-Amyloid Cardiomyopathy. We are hoping to learn more about the safety and effectiveness of the study drug and learn if it can help people with Transthyretin-Mediated-Amyloid Cardiomyopathy. During this study, you will be followed by the study team for three years with 18 doctors visits throughout the three years.