CALM3 and familial long QT syndrome: Through adopting a multidisciplinary approach to better understand three LQTS‐associated CaM mutants (D95V, N97I and D131H), we reveal the molecular mechanisms which explain the perturbed structure–function relationships of these CaM variants, how their altered structures hinder complex formation with Kv7.1, and how this modulation results in a LQTS‐compatible IKs.