Heart failure is a common clinical condition in cardiology, which has a significant influence on the prognosis of patients. Heart failure is currently divided into three entities: heart failure with reduced ejection fraction (HFrEF), heart failure with mildly reduced ejection fraction (HFmrEF), and heart failure with preserved ejection fraction (HFpEF). This chapter explains the diagnosis of heart failure and the therapy of different forms of heart failure according to current guidelines.