(A) In situ hybridization analysis showed that VDAC2 is expressed in embryonic hearts at 36 hpf (upper image) and 48 hpf (lower image). (B) Injection of 25 pg in vitro synthesized VDAC2 mRNA restored cardiac contractions in 52.9 ± 12.1% (n = 78) of 1-day-old tre embryos, compared to 21.8 ± 5.1% in uninjected siblings (n = 111). (C) Schematic diagram of myl7:VDAC2 construct (top). In situ hybridization analysis showed that TBF treatment induces VDAC2 expression in the heart (lower panel). (D) While only ~20% of myl7:VDAC2;NCX1hMO embryos have coordinated contractions (n = 116), 52.3 ± 2.4% of these embryos established persistent, rhythmic contractions after TBF induction of VDAC2 (n = 154). (E) On average, 71.2 ± 8.8% efsevin treated embryos have coordinated cardiac contractions (n = 131). Morpholino antisense oligonucleotide knockdown of VDAC2 (MOVDAC2) attenuates the ability of efsevin to suppress cardiac fibrillation in tre embryos (45.3 ± 7.4% embryos with coordinated contractions, n = 94). (F) Efsevin treatment restores coordinated cardiac contractions in 76.2 ± 8.7% NCX1MO embryos, only 54.1 ± 3.6% VDAC2zfn/zfn;NCX1MO embryos have coordinated contractions (n = 250). (G) Diagram of Zinc finger target sites. VDAC2zfn/zfn carries a 34 bp deletion in exon 3 which results in a premature stop codon (red asterisk). In situ hybridization analysis showing loss of VDAC2 transcripts in VDAC2zfn/zfn embryos. White arrowheads point to the developing heart.