The ventricular response to atrial fibrillation is irregularly irregular because of the large number of atrial impulses that transit the atrioventricular node, making the ventricle partially refractory to further impulses. Atrial fibrillation can cause a number of manifestations including excessive ventricular response with angina pectoris or hypotension in susceptible individuals, syncope, systemic embolization, fatigue, or anxiety. These features should be coded separately.