APOLLO-B: A Study to Evaluate Patisiran in Participants With Transthyretin Amyloidosis With Cardiomyopathy (ATTR Amyloidosis With Cardiomyopathy)

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