Study of AG10 in Amyloid Cardiomyopathy

Inclusion Criteria: 1. Have the ability to understand and sign a written informed consent form, which must be obtained prior to initiation of study procedures. 2. Be a male or female ≥18 to ≤90 years of age. 3. Have an established diagnosis of ATTR-CM with either wild-type transthyretin or a variant transthyretin genotype (assessed by genotyping, with patients with concurrent monoclonal gammopathy of undetermined significance requiring a confirmatory test using mass spectrometry) as defined by either positive endomyocardial biopsy or positive technetium pyrophosphate scan. 4. Have a history of heart failure evidenced by at least one prior hospitalization for heart failure or clinical evidence of heart failure (without hospitalization) requiring medical management. 5. Have New York Heart Association (NYHA) Class II-III symptoms. 6. Male patients and female patients of childbearing potential who engage in heterosexual intercourse must agree to use appropriate method(s) of contraception. 7. For patients taking cardiovascular medical therapy, with the exception of diuretic dosing, must be on stable doses (defined as no greater than 50% dose adjustment and no categorical changes of medications) for at least 2 weeks prior to Screening. Exclusion Criteria: 1. Acute myocardial infarction, acute coronary syndrome or coronary revascularization within 90 days prior to Screening. 2. Experienced stroke within 90 days prior to Screening. 3. Has hemodynamic instability at Screening or Randomization that, in the judgment of the Principal Investigator (PI), would pose too great a risk for participation in the study. 4. Has estimated glomerular filtration rate (GFR) \<30 mL/min/1.73 m2 at Screening. 5. Is likely to undergo heart transplantation within the next year. 6. Has confirmed diagnosis of light-chain amyloidosis. 7. Has abnormal liver function tests at Screening, defined as Alanine Aminotransferase (ALT) or Aspartate Aminotransferase (AST) \>3 × upper limit of normal (ULN) or total bilirubin \>2 × ULN. 8. Has abnormalities in clinical laboratory tests at Screening or Randomization that, in the judgment of the PI, would pose too great a risk for participation in the study. 9. Known hypersensitivity to study drug (AG10 or placebo), its metabolites, or formulation excipient 10. Current treatment with diflunisal, tafamidis, green tea, doxycycline, tauroursodeoxycholic acid (TUDCA)/Ursodiol, Patisiran or Inotersen within 14 days or 5 half-lives of the prior investigational agent (whichever is longer) prior to Screening. 11. Females who are pregnant or breastfeeding. Lactating females must agree to discontinue nursing before the study drug is administered. A negative serum pregnancy test at Screening and a negative urine pregnancy test at Randomization visit are required for female patients of childbearing potential. 12. In the judgment of the investigator, has any clinically significant ongoing medical condition that might jeopardize the patient's safety or interfere with the study, including participation in another investigational drug or investigational device study within the 30 days prior to Screening with potential residual effects that might confound the results of this study. 13. Has any laboratory abnormality or condition that, in the investigator's opinion, could adversely affect the safety of the patient or impair the assessment of study results. 14. Has any condition that, in the opinion of the investigator, would preclude compliance with the study protocol such as a history of substance abuse, alcoholism or a psychiatric condition. 15. Has participated in another investigational study within 14 days or 5 half-lives of the prior investigational agent (whichever is longer) prior to screening. Exceptions can be made in the case of observational and/or registry studies upon consultation with the Medical Monitor. 16. Current treatment with, or chronic use of, a proton pump inhibitor (PPI) or histamine-receptor 2 (H2) antagonist within 14 days or 5 half-lives of the prior agent (whichever is longer) prior to Screening.