The purpose of this study is to evaluate the safety of a drug called vutrisiran (amvuttra) and determine the effects it has on people with transthyretin amyloidosis (ATTR) with cardiomyopathy (either hereditary or wild type). ATTR amyloidosis is a condition that occurs when abnormal forms of a protein called transthyretin (TTR) deposits throughout the body, including in the heart and nerves. In the heart, they cause cardiomyopathy, where the heart muscle thickens and stiffens, affecting the heart’s ability to function properly. The study focuses on patients who participated in the patisiran parent studies (APOLLO-B Open-Label Extension or Patisiran Expanded Access Program), or who have completed the 24-month OLE Period in the vutrisiran parent study (ALN-TTRSC02-003). Researchers will assess the safety of vutrisiran for patients who are continuing treatment with vutrisiran or transitioning from treatment with patisiran. Participants will be administered vutrisiran every 3 months and will complete questionnaires to assess quality of life and describe ATTR amyloidosis symptoms. Blood and urine samples will be collected to monitor patients’ response throughout the study. Vutrisiran is a drug that helps block the body from making too much TTR. By reducing the body’s TTR levels, vutrisiran may, in turn, lower the build-up of amyloid in the heart and other organs of patients with ATTR amyloidosis. Vutrisiran is approved by the U.S. Food and Drug Administration (FDA) for the treatment of adults with ATTR, but its use in this study is considered investigational.