Heart Failure is a common disease associated with a high mortality rate. Patients often experience severely impaired quality of life. After the introduction of the angiotensin converting enzyme (ACE) inhibitors, beta blockers and mineralocorticoid receptor antagonists, sacubitril/valsartan was the first drug demonstrating a significant reduction of mortality. So far, there is no data on the application of sacubitril/valsartan in Swiss primary care. The longitudinal, non-interventional THESEUS study will document implementation and dosing of sacubitril/valsartan over a period of 6 months in patients with heart failure in follow-up in a primary care setting in Switzerland. The THESEUS study is expected to deliver valuable real-world data on the use of sacubitril/valsartan in Swiss primary care, its tolerability and safety profile as well as its impact on the usage of healthcare resources.