BACKGROUND The continuous flow (CF) left ventricular assist device (LVAD) has replaced the pulsatile flow (PF) LVAD because of its advantages of better patient survival and higher quality of life. However, "late-onset right ventricular failure (RVF)" after CF LVAD implantation has emerged as an increasing concern, but little is known about the mechanism. RESULTS We retrospectively analyzed the 3-month hemodynamic and echocardiographic data from 38 consecutive patients who had received CF LVADs, and from 22 patients who had received PF LVADs. Late-onset RVF was defined as persistent right ventricular stroke work index (RVSWI) <4.0g/m(2) at any rotation speed and after saline infusion test at 5 weeks after implantation of CF LVAD. Patients with late-onset RVF had significantly impaired exercise tolerance indicated by shorter 6-min walking distance and lower peak VO2, and worsened tricuspid regurgitation, together with enlargement of the RV under CF LVAD treatment (all P<0.05). Univariable analyses demonstrated that preoperative smaller LV diastolic diameter (LVDd) was the risk factor for late-onset RVF with a cutoff value of 64mm calculated by ROC analysis (area under curve, 0.925). In contrast, there was no correlation between preoperative LVDd and postoperative RVSWI in the PF LVAD group, though their preoperative background was worse than that of the CF group. CONCLUSIONS In the setting of preoperative small LVDd, CF LVAD may cause late-onset RVF by leftward shift of the interventricular septum.  (Circ J 2014; 78: 625-633).