Several critical Ca2+ handling components are dysfunctional in HF, including sarcoplasmic reticulum (SR) cardiac ryanodine receptor (RyR2, the calcium release channel) dysfunction and diastolic Ca2+ leak, reduced Ca2+ pump (the sarcoplasmic/endoplasmic reticulum Ca2+ ATPase, SERCA) activity, etc. (14). Here, RYR2 is linked to hydrops fetalis.