Few cases of atrial fibrillation can be completely excused from the possibility of having some impact of potential importance in the aviation environment. The clinical pattern in paroxysmal disturbance is very wide and possible incapacitating phenomena are mainly haemodynamic. In contrast, chronic atrial fibrillation is mostly well-tolerated with only minimal haemodynamic effect, but there is a risk of thromboembolism, suggesting the need for anti-thromboembolic treatment. A subgroup with chronic atrial fibrillation with a very low risk may be defined, allowing avoidance of anti-thromboembolic treatment and a positive attitude towards aeromedical certification. Such individuals are likely to be normotensive males, under the age of 60 years, with a normal left (and right) heart configuration on electrocardiography.