This study will test a medicine, NNC6019-0001, for people who have a heart disease due to TTR amyloidosis. It will look at how safe this medicine is in the long term and if it can reduce symptoms of a heart disease due to TTR amyloidosis, such as heart failure. It is an extension to a study called "A research study to look at how a new medicine called NNC6019-0001 works and how safe it is for people who have a heart disease due to TTR amyloidosis". Only participants who have completed that study will be invited for this new study. Participants will get NNC6019-0001, regardless of whether they got placebo or NNC6019-0001 in the first study. The study will last for up to 157 weeks (36 months/3 years).

Inclusion Criteria:

• Completed study intervention in NN6019-4940 and attended the last study visit (week 64; visit 16), and no later than 12 weeks after visit 16.
• Expected to be on stable doses of cardiovascular medical therapy 6 weeks prior to the enrolment visit.

Exclusion Criteria:

• A prior solid organ transplant.
• Presence or history of malignant neoplasm (other than basal or squamous cell skin cancer, in-situ 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 (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.
• Body weight greater than (>) 120 kilograms (kg) (264.6 pounds [lb]) at screening.

According to the Novo Nordisk disclosure commitment on novonordisk-trials.com