Methods and Results: This study was conducted at all 59 institutions that perform transcatheter mitral valve repair with the MitraClip system in Japan. The data of patients on whom transcatheter iASD closure was performed were collected. Of the 2,722 patients who underwent the MitraClip procedure, 30 (1%) required transcatheter iASD closure. The maximum iASD size was 9±4 mm (range, 3–18 mm). The common clinical course of transcatheter iASD closure was hypoxemia with right-to-left shunt or right-sided heart failure with left-to-right shunt. Of the 30 patients, 22 (73%) required transcatheter closure within 24 h following the MitraClip procedure, including 12 with hypoxemia and 5 with right-sided heart failure complicated with cardiogenic shock. Of the 5 patients, 2 required mechanical circulatory support devices. Twenty-one patients immediately underwent transcatheter iASD closure, and hemodynamic deteriorations were resolved; however, 1 patient died without having undergone transcatheter closure.