Background: Refractory arrhythmias caused by right ventricular (RV) volume overload resulting from pulmonary regurgitation are the main concern in adult patients after repair of tetralogy of Fallot (TOF). Early pulmonary valve replacement (PVR) may prevent irreversible RV dysfunction and refractory arrhythmias, so the present study evaluated the PVR outcomes in adult patients with a severely dilated RV (d-RV) and refractory arrhythmias after TOF repair. Methods and Results: Three TOF patients with a d-RV and tachyarrhythmias underwent PVR between the ages of 28 and 38 years. All had a d-RV (RV end-diastolic volume index (RVEDVI) >200 ml/m 2 ) with a polymorphic nonsustained ventricular tachycardia (NSVT). Atrial tachycardia (AT) was identified in 2 patients and they underwent radiofrequency catheter ablation. The arrhythmias in all 3 were refractory to antiarrhythmic drugs. One year after PVR, the RVEDVI, left ventricular ejection fraction, right atrial pressure, cardiac index, cardiothoracic ratio, brain natriuretic peptide levels, and peak V• O2 improved in all, but without normalization. During the 2.6-3.8 year follow-up, all experienced tachyarrhythmias (NSVT or AT), which were controlled with medication. Conclusions: PVR may be beneficial for refractory arrhythmias, even in TOF patients with a d-RV, but it is difficult to completely normalize the hemodynamics and resolve the arrhythmogenicity. (Circ J 2009; 73: 2135 -2142