A Research Study to Look at How a New Medicine Called NNC6019-0001 Works and How Safe it is for People Who Have Heart Disease Due to Transthyretin (TTR) Amyloidosis

Inclusion Criteria:

Male or female.
Age greater than or equal to (>=) 18 to less than (<) 85 years at the time of signing informed consent.
Have an established diagnosis of Transthyretin amyloid cardiomyopathy (ATTR CM) with either wild-type transhyretin (TTR) or hereditary transthyretin (TTR) genotype as per local standards.
Expected to be on stable doses of cardiovascular medical therapy 6 weeks prior to the randomisation visit.
Known end-diastolic interventricular septal wall thickness greater than or equal to (>=) 12 millimeters (mm).
Presently classified as New York Heart Association (NYHA) Class II-III.
N-terminal-pro brain natriuretic peptide (NT-proBNP) concentration greater than or equal to (>=) 650 picograms per milliliter (pg/mL) in sinus cardiac rhythm and greater than (>) 1000 pg/mL in atrial fibrillation at screening.
Completed greater than or equal to (>=) 150 meters to less than or equal to (<=) 450 meters on the 6-minute walk test (MWT) at screening.
Estimated glomerular filtration rate (eGFR) greater than or equal to (>=) 25 milliliter per minute per 1.73 meter square (mL/min/1.73 m^2) at screening.

Exclusion Criteria:

Cardiomyopathy not primarily caused by transthyretin amyloid cardiomyopathy transthyretin amyloid cardiomyopathy (ATTR CM), for example, cardiomyopathy due to hypertension, valvular heart disease, or ischemic heart disease.
A prior solid organ transplant.
Planned solid organ transplant during the study.
Presence or history of malignant neoplasm (other than basal or squamous cell skin cancer, insitu carcinomas of the cervix, or in-situ/high grade prostatic intraepithelial neoplasia (PIN) or low-grade prostate cancer) within 5 years before screening.
Current treatment with calcium channel blockers with conduction system effects (example [e.g.], verapamil, diltiazem). The use of dihydropyridine calcium channel blockers is allowed. The use of digoxin will only be allowed if required for management of atrial fibrillation with rapid ventricular response.
Acute coronary syndrome, unstable angina, stroke, transient ischemic attack (TIA), coronary revascularization, cardiac valve repair, or major surgery within 3 months of screening.
Body weight >120 kilogram (kg) (264.6 pounds [lb]) at screening.
History of contrast allergy or adverse reactions to gadolinium-containing agents.