SCN5A and hydrops fetalis: Of note, SCN10A mRNA expression in tissue from non-failing and HF hearts, as well as isolated cardiomyocytes from human HF hearts was found to be much lower than SCN5A. Further, RT-qPCR experiments revealed that a relevant part of SCN10A mRNA in the heart originates from cardiomyocytes (Supplementary information, Supplementary Figs. 1,  2).