Micelle-forming amphiphilic block copolymers for use in targeting cardiac cells (e.g. fibrotic cells) of a subject suffering from heart failure, micelles containing the micelle-forming amphiphilic block copolymers together with a cardioactive agent, and related compositions and methods for treating or preventing heart failure, e.g. heart failure with preserved ejection fraction (HFpEF) also known as diastolic heart failure.