Gender
All
Age Group
18 Years to 85 Years
Accepting Healthy Volunteers
No
Inclusion Criteria:
* Documented diagnosis of ATTR amyloidosis with cardiomyopathy, classified as either hereditary ATTR amyloidosis with cardiomyopathy or wild-type ATTR amyloidosis with cardiomyopathy
* Medical history of heart failure with at least 1 prior hospitalization for heart failure, or current clinical evidence (signs and symptoms of heart failure)
* Clinically stable with no cardiovascular related hospitalizations within 6 weeks of study start
* Has never taken tafamidis before (tafamidis naïve) or currently on tafamidis for ≥6 months with evidence of disease progression while on tafamidis treatment
* Able to complete ≥150 m on the 6-minute walk test
* Screening N-terminal pro B-type natriuretic peptide (NT-proBNP), a blood marker of heart failure severity, \>300 ng/L and \<8500 ng/L; in participants with permanent or persistent atrial fibrillation, screening NT-proBNP\> 600 ng/L and \<8500 ng/L
Exclusion Criteria:
* Known primary amyloidosis (AL) or leptomeningeal amyloidosis.
* Received prior TTR lowering treatment
* New York Heart Association heart failure classification of III and at high risk
* New York Heart Association heart failure classification of IV
* Neuropathy requiring cane or stick to walk, or is wheelchair bound
* Estimated glomerular filtration rate (eGFR) \<30 mL/min/1.73m\^2
* Abnormal liver function
* Has hepatitis B, hepatitis C or human immunodeficiency virus (HIV) infection
* Has non-amyloid disease that significantly affects ability to walk (e.g., severe chronic obstructive pulmonary disease, severe arthritis, or peripheral vascular disease affecting ambulation)
* Prior or planned heart, liver, or other organ transplant
* Other cardiomyopathy not related to ATTR amyloidosis