Background:Size-mismatched heart transplantation (HTx) is associated with a risk of stenosis of the caval anastomosis site or low cardiac output syndrome. We developed a modified bicaval anastomosis technique (mBCAT) that achieved an adjustable caval anastomosis to compensate for size mismatch. This study was performed to validate the rationale of the mBCAT for size-mismatched HTx.Methods and Results:This institutional consecutive series involved 106 patients who underwent HTx with the mBCAT during an 18-year period. The cohort was divided into 3 groups according to the donor-to-recipient body weight ratio: <0.8, undersized group (n=17); 0.8–1.3, size-matched group (n=68); and >1.3, oversized group (n=21); outcomes were compared. The undersized, size-matched, and oversized groups showed no significant differences in the rate of mild or worse echocardiographic tricuspid regurgitation at 1 month 1 (5.8%), 7 (10.2%), and 1 (4.8%), respectively; P=0.87 or the survival rate at 10 years 100%, 93.9%, and 100%, respectively; P=0.25. The right heart catheter study revealed no pressure gradient across the orifices of both cavae in any patient. Additionally, the cardiac index immediately post-HTx was significantly low in the undersized group (P=0.008), but was similar to the other groups at 6 months post-HTx (P=0.16).Conclusions:The mBCAT prevented caval anastomosis-related complications in size-mismatched HTx and achieved excellent hemodynamics regardless of donor size.