This clinical trial is focused on studying a condition known as Transthyretin Amyloidosis with Cardiomyopathy, often referred to as ATTR Amyloidosis with Cardiomyopathy. This is a disease where abnormal proteins called amyloids build up in the heart, affecting its function. The study is evaluating a treatment called Patisiran, which is administered as a solution for infusion. Patisiran is designed to target and reduce the production of transthyretin, a protein that can misfold and form amyloid deposits in the heart.

The purpose of the study is to assess how effective and safe Patisiran is compared to a placebo in improving the ability to walk, as measured by a test called the 6-minute walk test. Participants in the study will receive either Patisiran or a placebo through an intravenous infusion, which means the medication is given directly into a vein. The study will last for about 12 months, during which participants will have regular check-ups to monitor their health and the effects of the treatment.

Throughout the study, researchers will also look at other health outcomes, such as changes in symptoms and overall quality of life, using tools like the Kansas City Cardiomyopathy Questionnaire. The study aims to provide valuable information on whether Patisiran can help improve the lives of people with ATTR Amyloidosis with Cardiomyopathy by reducing symptoms and improving heart function.