All work was approved by the Institutional Review Board (IRB) at the University of Arizona and the IRB at the Children’s Hospital of Philadelphia. Well-characterized left ventricular tissue from three healthy donor hearts as close in age as possible to the patient was obtained from the Sydney Heart Bank (26) (University of Sydney, Australia) following approval of the Human Research Ethics Committee. Their sample codes are 5.114, 7.050, and 4.152. The tissue was transported and stored in liquid nitrogen.