The physiopathology of right ventricular failure after repair of tetralogy of Fallot is complex. While primarily reflecting chronic volume overload resulting from pulmonary regurgitation, its determinants reflect a varied contribution of different boundary conditions. The competence of the outflow tract, right ventricular afterload, and the integrity of right ventricular diastolic performance are all crucial elements to the long-term responses of the right ventricle. When adverse, chronic right ventricular volume overload may lead to exercise intolerance, congestive cardiac failure, and both atrial and ventricular arrhythmia. Indeed, there appears to be a close relationship between the mechanical properties of the right ventricle and its electrical stability. In this chapter the determinants of pulmonary incompetence and its secondary effects on right ventricular function and performance, and mechano-electric interactions will be discussed.