Mutant hearts exhibited increased levels of the NCX1 Na+/Ca2+ exchanger (Figure 3A) and the NHE1 Na+/H+ exchanger (Figure 3B), which is increased in cardiac hypertrophy and can affect Ca2+ handling via NCX1-mediated Na+-loading (Karmazyn et al., 2008). The gene discussed is SLC9A1; the disease is cardiac hypertrophy.