Based on this method developed by Colecraft's laboratory (Aromolaran et al., 2014), we observed that KCNQ1 surface density (ECFP+Alexa Fluor 647 labelled) was 35.0 ± 1.2% (of total KCNQ1 channels, ECFP only, n = 5) and that LQTS‐associated CaM variants did not significantly alter the percentage of channels at the plasma membrane. This evidence concerns the gene CALM3 and familial long QT syndrome.