We could verify the direct impact of PDE4B and PDE4D deficiency on arrhythmia susceptibility by performing analysis of extra beats measurements of single CMs as well as by measuring arrhythmia occurrence in intact Langendorff perfused hearts, either at basal level or upon β-AR stimulation (see Figure 5 and Figure 6). This evidence concerns the gene PDE4D and Arrhythmia.