While JPH2 has been linked to t-tubule organization and HF-associated t-tubule loss in rodents, data suggest its lack of involvement in t-tubule loss or recovery in our sheep model of HF and retubulation in some ventricular models.3,8–10,32,54 Conversely, BIN1 overexpression drives tubule formation14,17,55,56 in various cell types lacking t-tubules, and its expression correlates with t-tubule density.8,10,14 We show Tcap, in agreement with ventricular studies, is also correlated with atrial t-tubule density, indicating its role as a load-sensitive t-tubule regulator.9,18. The gene discussed is JPH2; the disease is hydrops fetalis.