(A) Representative echocardiography images of NPY^–/+ and NPY^–/– mice. (B) Cardiac left ventricular mass (LVM). (C) Ventricular ejection fraction (EF) percentage. (D) HW. (E) HW/BW ratio. (F) Representative electrocardiogram recorded in NPY^–/+ and NPY^–/– mice. (G) Heart rate (HR). (H) QT interval. (I) Representative AP recorded in WT, NPY^–/+, and NPY^–/– cardiomyocytes. (J) APD₉₀. (K) AP duration measured at 50% repolarization (APD₅₀). (L) RMP. (M) Superimposed representative APs recorded at baseline and after exogenous NPY (100 nM) application. (N) APD₉₀ at baseline and after exogenous NPY application in each group. (O) Representative I_Ca,L traces recorded in NPY^–/+ and NPY^–/– cardiomyocytes. (P) Current-voltage relationship plot of I_Ca,L. (Q) Representative I_to traces recorded in NPY^–/+ and NPY^–/– cardiomyocytes. (R) I_to density. (S) Representative I_K,slow traces recorded in NPY^–/+ and NPY^–/– cardiomyocytes. (T) I_K,slow density. (U) Representative I_ss traces recorded in NPY^–/+ and NPY^–/– cardiomyocytes. (V) I_ss density. Currents were normalized to cell capacitance and are expressed as current density (pA/pF). Data are shown as the mean ± SD, with cardiomyocyte data nested within mice. *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001. Comparisons between two groups were performed using 2-tailed nested t test, Student’s t test, or the Mann-Whitney test, as appropriate. Comparisons among multiple groups were performed using nested 1-way ANOVA, ordinary 2-way ANOVA, mixed-effects analysis, or the Kruskal-Wallis test, as appropriate.