Depletion of rbm24a and rbm24b compromise cardiac myocardial development. The expression patterns of cardiac markers were analyzed in rbm24 morphants and uninjected controls at 72 hpf. Ventral and lateral images of the heart are shown with a dotted line marking the boundary between heart chambers. By myl7 expression of the entire heart, uninjected controls possess looped hearts with defined ventricle and atrium chambers (A, B) in contrast to unlooped hearts for both rbm24 morphants. rbm24a morphants displayed linear presumptive ventricle and an incompletely formed presumptive atrium (C, D). rbm24b morphants displayed a linear presumptive atria and ventricle (E, F). myh6 marking the atrium displayed a looped atrium in controls (G, H) with linear atrium in rbm24a (I, J), and rbm24b morphants (K, L). vmhc expression demarks looped ventricles in controls (M, N). rbm24a morphants displayed little expression bound to an unlooped heart tube where expression extends to the presumptive atrium (O, P). Almost no vmhc expression is detectable in rbm24b morphants (Q, R). v, ventricle region; double arrow, ventricular expression a, atrium region; solid black arrow, atrial expression.