Adult male guinea pigs (800–1000 g; n = 3) were anesthetized and their ventricles isolated as previously described (Veeraraghavan and Poelzing, 2008 (link); Veeraraghavan et al., 2012 (link), 2013 (link)). Tissue blocks cut from these ventricles were embedded in OCT and frozen for cryosectioning. Sections (5 μm) were cut from frozen tissue blocks, fixed in 2% paraformaldehyde at room temperature for 5 min, and immunolabeled as previously described (Veeraraghavan et al., 2015 (link)) with mouse anti-Cx43 (MAB3067, 1:100; Millipore, Billerica, CA) and rabbit anti-Nav1.5 (1:100; kindly provided by Peter Mohler, SBS-Physiology & Cell Biology, The Ohio State University). Samples were then labeled with goat anti-rabbit Alexa 647 (1:4000) and donkey anti-mouse Cy3b (1:100) secondary antibodies. STORM images were obtained using a Vutara 350 microscope equipped with biplane 3D detection (Juette et al., 2008 (link); Mlodzianoski et al., 2009 (link); Deschout et al., 2014 (link)) and fast scientific complementary metal-oxide-semiconductor imaging, achieving 20-nm xy- and 50-nm z-resolution. Volumes imaged had a surface extent of 10 × 10 to 15 × 15 μm and spanned between 3 and 5 μm in the z-dimension. Localization of particles was accomplished with a precision of 10 nm. Registration of the two color channels was achieved using a transform calculated from the localized positions of several TetraSpeck Fluorescent Microspheres (ThermoFisher Scientific, Carlsbad, CA) scattered throughout the field of view, similar to a previously described approach (Churchman and Spudich, 2013 ).