A Study to Evaluate the Safety of mRNA-0184 in Participants With Heart Failure

Key Inclusion Criteria:

• Documented diagnosis of heart failure (HF) based on medical records.

• Left ventricular ejection fraction (LVEF) ≥ 35% and < 50% at Screening, ordocumented within the 3 months before Screening, measured by transthoracicechocardiogram (TTE) or cardiac magnetic resonance imaging (MRI).

• New York Heart Association (NYHA) HF Class I or II.

• On a stable regimen of cardiovascular medication(s) for a duration of at least 4weeks before Screening.

Key Exclusion Criteria:

• Hospitalized for cardiovascular causes within 3 months before Screening.

• Decompensated HF, acute myocarditis, hypertrophic and/or restrictive/constrictivecardiomyopathy, or moderate or severe valvular heart disease (as classified byechocardiography) at Screening or within the 3 months before Screening. Moderatetricuspid regurgitation is not exclusionary. Congenital heart disease as the primaryetiology for heart failure will be excluded.

• Symptoms of angina pectoris at Screening.

• Severe obstructive or restrictive pulmonary pathology, including chronic obstructivepulmonary disease Gold Stage III or IV, current use of oxygen therapy, or Group 1, 3, 4, or 5 pulmonary hypertension. Group 2 pulmonary hypertension is notexclusionary.

• History of sustained ventricular tachycardia or atrial fibrillation/atrial flutterwith a ventricular response ≥ 110 beats per minute (bpm) at the time of Screening.

• History of hypersensitivity to any components of the investigational product (IP).

• Participant has received or is expected to receive a COVID-19 vaccination within 7days of the planned date of IP administration.

• For SAD cohort participants to be rolled over into the MAD stage, have experienced adose-limiting toxicity (DLT) in a SAD cohort.

• Participation in another clinical study of another IP within 30 days beforeScreening or within 5 terminal elimination half-lives of the IP, whichever islonger.

• Any other clinically significant medical condition that, in the Investigator'sopinion, could interfere with the interpretation of study results or limit theparticipant's participation in the study, including poorly controlled diabetesmellitus.