(A) Representative Ca2+ imaging and plot of caffeine-induced Ca2+ transient in WT and sorcin KO cardiomyocytes. WT τcaf f= 2369 ms, KO τcaff= 1758 ms. (B) NCX rate (KNCX). WT-basal n=10, KO-basal n=9; WT-iso n=12, KO-iso n=13. (C) Protocol for recording INCX and representative INCX of WT and sorcin KO cardiomyocytes under isoproterenol stimulation. (D) I–V curve of INCX under basal condition. WT-basal n=9, KO-basal n=8 (E) I–V curve of INCX under isoproterenol stimulation. WT-iso n=9, KO-iso n=9. *, p<0.05 vs. WT.