It remains to be determined whether balloon pulmonary angioplasty (BPA) improves biventricular cardiac functions and pulmonary flow in patients with chronic thromboembolic pulmonary hypertension (CTEPH). We enrolled 30 consecutive patients with inoperable CTEPH who underwent BPA, and carried out serial cardiac magnetic resonance imaging (CMR; M/F, 9/21; median age, 65.2 years). No patient died during the treatment or follow-up period. BPA significantly improved WHO functional class (III/IV, 83.0 to 4.0%), 6-min walking distance (330.2±168.7 to 467.3±114.4 m), mean pulmonary artery pressure (40.8±10.7 to 23.2±4.94 mmHg), pulmonary vascular resistance (9.26±4.19 to 3.35±1.40 WU) and cardiac index (2.19±0.64 to 2.50±0.57 L·min·m(2); all P<0.01). CMR also showed improvement of right ventricular (RV) ejection fraction (EF; 41.3±12.4 to 50.7±8.64%), left ventricular (LV) end-diastolic volume index (72.1±14.0 to 81.6±18.6 ml/m(2)) and LV stroke volume index (41.0±9.25 to 47.8±12.3 ml/m(2); all P<0.01). There was a significant correlation between change in RVEF and LVEF (Pearson's r=0.45, P=0.01). Average velocity in the main pulmonary artery was also significantly improved (7.50±2.43 to 9.79±2.92 cm/s, P<0.01). BPA improves biventricular functions and pulmonary flow in patients with inoperable CTEPH. (Circ J 2016; 80: 1470-1477).