(A) Representative TUNEL-stained thin myocardial sections in 3-week-old untreated, vehicle-treated, and JQ1-treated WT mice along with untreated, vehicle-treated, and JQ1-treated Myh6-Cre LmnaF/F mouse hearts. Nuclei were counterstained with DAPI. (B) Corresponding quantitative data showing percentage of TUNEL-labeled nuclei in myocardial sections in untreated (black dots; n = 6), vehicle-treated (yellow dots; n = 3), and JQ1-treated (orange dots; n = 3) WT and untreated (red dots; n = 5), vehicle-treated (blue dots; n = 7), and JQ1-treated (green dots; n = 6) Myh6-Cre LmnaF/F mouse hearts. P values were calculated using 2-way ANOVA and Tukey’s post hoc test for comparisons; *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001. (C) Transcript levels of selected BRD4 target genes involved in apoptosis, as quantified by RT-qPCR, are depicted in 3-week-old untreated (black dots; n = 4) and JQ1-treated (orange dots; n = 5) WT mice, and in untreated (red dots; n = 6) and JQ1-treated (green dots; n = 8) Myh6-Cre LmnaF/F mouse hearts. P values shown were obtained with ordinary 1-way ANOVA or Kruskal-Wallis; *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001.