Background: Membrane-associated guanylate kinase (MAGUK) proteins are important determinants of ion channel organization in the plasma membrane of various cell types. In the heart, the MAGUK protein SAP97 was found to interact with several ion channels (Nav1.5, Kir2.x, Kv4.x, Kv1.5) via their PDZ-domain-binding motif, and was proposed to regulate their function and localization. In order to better understand the role of SAP97 in the mouse heart, we generated a genetically modified mouse model where SAP97 was constitutively suppressed in cardiomyocytes, and studied the consequences on cardiac ion channel function.Methods: To delete SAP97 in the mouse heart, SAP97fl/fl mice were generated, where LoxP sequences flank exons 1 through 3 of the SAP97 gene. SAP97fl/fl mice were bred with αMHC-Cre mice (where the cardiac-specific alpha myosin-heavy chain (Myh6) promoter drives expression of Cre recombinase) to generate αMHC-Cre/SAP97fl/fl mice with a cardiac-specific deletion of SAP97. Whole hearts and isolated cardiomyocytes from 10-13 week old mice were used for the experiments. SAP97 protein and mRNA expression levels were measured by Western-blot and quantitative RT-PCR. Sodium (INa) and potassium (IK1, Ito, and IKur) currents, as well as action potentials (AP) were recorded in isolated cardiomyocytes using the patch-clamp technique. Student’s t-test was used to compare means between αMHC-Cre/SAP97fl/fl and SAP97fl/fl groups.Results: Western blots performed on whole-heart lysates showed a 71±4% decrease in SAP97 protein levels of αMHC-Cre/SAP97fl/fl hearts compared to SAP97fl/fl control hearts (n=4, p<0.05). SAP97 mRNA transcript levels were decreased by 80±2% in αMHC-Cre/SAP97fl/fl cardiomyocytes compared to controls (n=4, p<0.05). AP recordings showed no differences in AP maximal upstroke velocity and time to peak, suggesting that INa was not altered. In contrast, AP duration (APD) was greatly increased in αMHC-Cre/SAP97fl/fl cardiomyocytes (respectively by 1.9±0.3, 2.3±0.4, and 2.1±0.2 -folds for APD30, APD50, and APD90; n=10, p<0.05). This was consistent with the decreases observed in IK1, Ito, and IKur potassium currents and the absence of effect on INa.Conclusions: These data suggest that ablation of SAP97 in the mouse heart mainly alters potassium channel function and/or localization. Additional experiments are needed to elucidate whether ion channel expression at the plasma membrane and/or unitary conductance are modified.