Slow heart rate may contribute to cardiac edema in rbm24 morphants. Heart rates were determined for uninjected control, rbm24a and rbm24b morphant embryos at 48, 72 & 96 hpf and significance was ascribed from a t-test statistic. 50 embryos were examined for each condition at each time point. At all time-points the heart rate of rbm24a morphants was significantly lower than controls where P < 2 × 10-5. At 48 hpf rbm24b morphants had significantly lower heart rates than controls (P = 1 × 10-32). The heart rates for rbm24b morphants then rose to rates not different from controls by 72 hpf and 96 hpf (P > 0.12) while maintaining the features of the morphant phenotype. Error bars here are standard error. *** P < 0.001.