KCNN1 and hydrops fetalis: Our main results are: (i) principal component analysis yields clear clustering of atrial vs. LV samples, and of diseased vs. non-diseased myocardium; (ii) in non-diseased hearts, only SK1 (but not SK2 and SK3) channels are expressed to a significantly larger extent in atrial (RAA and LA) than in LV tissue samples; (iii) HF is associated with an upregulation of SK3 channel, and AF is associated with a downregulation of SK2 isoform.