Summary of cardiac phenotypes observed in wildtype and TMEM161B knockout (KO) mouse embryos. At 14.5 dpc, TMEM161B KO embryos have VSDs and atrial and ventricular defects (AVSD, cyan asterisks). At 17.5 dpc, TMEM161B KO embryo hearts have altered morphology (although no reported VSD or AVSD), with thickened interventricular septum (cyan scale bar) and increased cell number. Isolated cardiomyocytes exhibit altered Ca.²⁺ oscillation, compared with wildtype littermates. At 18.5 dpc, the ventricular walls of TMEM161B KO embryonic hearts are considerable thicker (cyan scale bars) and, in some instances, almost entirely occlude the chamber lumen. Phenotypic summary derived from published data (Koopman et al. 2021; Spielmann et al. 2022) and IMPC data (http://www.mousephenotype.org/data/embryo)