S3A cardiomyocytes show an increased duration of [Ca ²⁺ ] _i transients compared to WT cardiomyocytes, which was prevented by Cx43 hemichannel blockade. (A and B) Representative line scan images from WT (top) and S3A (bottom) myocytes under field stimulation (1 Hz) in control conditions (A) and after incubation with Gap19 peptide (200 µM; B). The traces above each line scan represent the spatially averaged time curse of [Ca²⁺]_i for each image. The number in parentheses indicates biological replicates. We analyzed three to five cells per mouse. (C and D) Amplitude quantification (C) and decay time 90% (ms) quantification (D). The number in parentheses indicates the n value. P = 0.0012 WT vs. S3A; P = 0.0067 S3A vs. S3A + Gap19. Comparisons between groups were made using nested-ANOVA. The number in parentheses indicates biological replicates. We analyzed three to five cells per mouse.