The aim of this observational study is to evaluate safety and therapeutic adherence during anticoagulant prophylaxis with apixaban in patients with nonvalvular atrial fibrillation. The main questions it aims to answer are:

• What is the incidence of major bleeding and clinically relevant non-major bleeding during anticoagulant prophylaxis with apixaban in patients with nonvalvular atrial fibrillation?
• What is therapy adherence during anticoagulant prophylaxis with apixaban in patients with nonvalvular atrial fibrillation?
• What is frequency and types of other adverse reactions, excluding bleeding, during anticoagulant prophylaxis with apixaban in patients with nonvalvular atrial fibrillation? Participants will be followed for six months through four measurements. The first and fourth measurements will be performed in person, while the remaining measurements can also be recorded by telephone, if the patient's condition allows. Any bleeding or serious adverse reactions to the medication being administered will be recorded immediately, through unscheduled measurements. Adverse reactions will be recorded at each measurement. Adherence to the medication being administered will be evaluated using the BARS scale.

Inclusion Criteria:

• Patients over 18 years of age.
• Hemodynamically stable patients.
• Patients with non-valvular atrial fibrillation.
• Patients in whom the investigator, based on clinical assessment makes a decision to introduce apixaban therapy.
• Patients who are on apixaban therapy for the first time

Exclusion Criteria:

• Positive history of angioneurotic edema.
• Active, clinically significant bleeding.
• Congenital or acquired bleeding disorder.
• The presence of a malignant tumor.
• Current or recent presence of gastrointestinal ulcer.
• The presence of established or suspected esophageal varices.
• Positive history of arteriovenous malformations, vascular aneurysms or intraspinal and intracerebral vascular anomalies.
• Patients with artificial heart valves.
• Liver cirrhosis and active liver disease associated with coagulopathy and clinically significant risk of bleeding.
• Dialysis patients (GFR <15 ml/min).
• Simultaneous use of other anticoagulants.
• Pregnancy and breastfeeding.
• Patients who previously used apixaban in therapy.

Withdrawal Criteria:

• Deterioration of the clinical picture of the underlying disease that requires discontinuation of investigational therapy.
• Development of serious adverse events that require discontinuation of therapy.
• Occurrence of pregnancy.
• Development of another disease that affects the course of research.

Eligible patients from participating centers from Bosnia and Herzegovina who are treated on an outpatient basis or in a hospital setting.