Since HF patients exhibit both diastolic SR Ca2+ leak and reduced systolic Ca2+ release, we decided to study two accessory proteins that play important roles in diastolic and systolic RyR2 regulation: calstabin-2 (also known as FKBP1B or FKBP12.6) and calmodulin (CaM), respectively27. The gene discussed is FKBP1B; the disease is hydrops fetalis.