Histology of swim bladder development of silent heart morphants with heart failure (E-H), and embryos injected with control MO (A-D), at 48 to 120 hpf. Control embryos developed swim bladders normally. Silent heart morphants underwent normal swim bladder budding (E), elongation, and initial growth (F), however, subsequent growth beginning at 96 hpf was disrupted (G-H). By 120 hpf the silent heart morphant swim bladder is significantly smaller and has thick-walled morphology (H) compared to control (D). Black dotted outlines indicate developing swim bladder, scale bars represent 100 μm.