This study will examine if maridebart cafraglutide as an adjunct to standard of care will lead to a reduction in heart failure (HF) events such as HF hospitalizations and urgent HF visits, cardiovascular (CV) deaths and improvement in HF symptoms in participants with HF with preserved ejection fraction (HFpEF) and HF with mildly reduced ejection fraction (HFmrEF) who are obese. This is a phase 3, global, multicenter, 2-part study with a double-blind period and an open-label extension (OLE). The study is event-driven, and Part 1 will conclude when approximately 850 primary endpoint events have occurred.