WT, CD38KO and CD38CI (catalytically inactive) male adult mice (6–8-month-old) were submitted to telemetry implant surgery and their ECG was recorded in the 3rd and 4th day after surgery. (a) Representative 1 second ECG tracings from WT, CD38KO, and CD38CI mice. (b) The graphs show heart rate (HR) and three indexes of HR variability (HRV): root mean square of successive differences (RMSSD), standard deviation of normal-normal RR intervals (SDNN), and variability coefficient (VC). HR is lower and HRV is higher in CD38KO and CD38CI groups compared to WT group. Data are mean ± SEM (N=6 mice/group), analyzed by unpaired two-sided t-test, *P<0.05.