The objective of this study is to determine the association of clinically prescribed, on-label, TTR stabilizing therapy (e.g. tafamidis or acoramidis) with levels of circulating transthyretin amyloid aggregates (TAAs, a surrogate for amyloid disease activity) measured serially over time in patients with transthyretin cardiac amyloidosis (ATTR-CA). To accomplish this objective, the hypothesis that TTR stabilizing therapy will be associated lower circulating TAAs over time will be tested. Completion of this study will advance the understanding of the influence of ATTR-CA treatments on circulating evidence of amyloidosis and justify the role of blood testing to monitor treatment response in patients with ATTR-CA.

Inclusion Criteria:

• Men and women ages 30-80 who have symptomatic ATTR-CA as determined by a history of HF (this will be assessed by study personnel and defined as : 1) history of hospitalization within the previous 12 months for management of HF; 2) an elevated B-type natriuretic peptide level ≥100 pg/mL or NT-proBNP ≥360 pg/mL within the previous 12 months; or 3) a clinical diagnosis of HF from a treating clinician)
• ATTR-CA previously diagnosed histologically by amyloid staining and tissue typing with immunohistochemistry or mass spectrometry or by bone scintigraphy in without abnormal M-protein
• TTR gene sequencing confirming the TTR genotype has resulted or is pending
• Enrollment will be stratified by n/N=30/50 starting on-label TTR-stabilizing therapy (e.g. tafamidis) within 5 days after enrollment or by n/N=20/50 of those currently taking TTR-stabilizing therapy

Exclusion Criteria:

• Other known causes of cardiomyopathy
• History of light-chain cardiac amyloidosis
• Cardiac transplantation
• Liver transplantation
• Has taken patisiran in the past 90 days, or inotersen in the past 180 days, has ever taken vutrisiran, or is participating in a clinical trial for ATTR treatments
• Estimated glomerular filtration rate ≤30 mL/min/1.73 m2
• Anticipated gaps in ATTR-CA treatment for 3 months after enrollment

ATTR-CA patients with a diagnosis of heart failure.