This document summarizes the 2021 ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure. It discusses changes and recommendations for several areas: HFrEF, HFmrEF, HFpEF, advanced HF, and acute HF. For HFrEF, it emphasizes initiating the four key drug therapies as quickly as possible. For HFmrEF, it introduces a new definition and recommends treatments similar to HFrEF. For HFpEF, it stresses actively searching for underlying causes and trial results.