The study team will use small pieces of human hearts which are removed as part of a required surgical procedure to study different objectives. One of the objective is how calcium ions pass through the membrane of heart cells in order to tell the heart cell how much force to contract with when the heart beats. Investigators will also study the proteins and RNA of these pieces to determine how the newborn heart cells control their force of contraction differently from adult heart cells. Investigators hypothesize that infant hearts have different regulation of calcium entry than adult hearts. The study team also wants to study combinations of 3D cardiac spheres with multiple environmental cues that can improve functional and metabolic maturation of Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) and generate a more clinically relevant cell model.