To the Editor We appreciate the thoughtful editorial by Shah and Vaccarino1 in JAMA Psychiatry in response to our prospective investigation of the association of predeployment heart rate variability (HRV) with postdeployment posttraumatic stress disorder (PTSD) in military service personnel.2 We agree that the findings are in need of replication by other groups, particularly with attention to limitations inherent in HRV indices including the low frequency to high frequency ratio, among others.3 Shah and Vaccarino1 mentioned several concerns, briefly addressed here.