Heart failure is a disease with multiple causes but uniform clinical picture. Compromised cardiac activity triggers many compensatory mechanisms, one of which is the renin-angiotensin-aldosterone system, which can lead to negative effects when activated chronically. Modulation of the renin-angiotensin-aldosterone-system is therefore needed in the treatment of heart failure to prevent exacerbation of the disease. Such modulation can be achieved with different classes of drugs, such as ACE-I, ARBs, ARNI, MRA, and renin inhibitors. This modulation of the renin-angiotensin-aldosterone-system has proven to have favourable effects on the mortality and morbidity of heart failure patients, and is therefore a standard treatment.