TLX2 and hydrops fetalis: The finding in the present study that, despite the reported loss of t-tubules in HF atrial myocytes [27], the relationship between NCX current and [Ca2 +]i is reduced in HF is consistent with either a reduction of NCX expression at the cell surface in HF or, if this is unaltered, an increased density of NCX on the t-tubules which have subsequently been lost in HF.