Demonstration of electrical dissociation of the left superior pulmonary vein from the left atrium after catheter ablation. Figure shows electrogram recordings taken during pulmonary vein isolation. Small arrows point to far-field atrial potential on the circular mapping catheter (Lasso 1–20) during sinus rhythm. The large arrows point to slow, dissociated pulmonary vein potentials, indicating complete electrical isolation of the vein.