Heart rate variability (HRV) associated with parasympathetic activity (i.e., cardiac vagal tone) is reduced in posttraumatic stress disorder (PTSD), but possible confounding effects of respiration have not been studied sufficiently. Further, reduced parasympathetic inhibition might contribute to elevated heart rate (HR) in PTSD. Finally, reduced HRV in PTSD might extend to intimate partners, given their chronic stress exposure. In 65 couples (male Veterans, female partners), elevated PTSD symptomatology (n = 32; 28 met full DSM IV criteria, 4 fell slightly short) was documented by structured interview and self-reports. Baseline HR, high-frequency HRV (HF-HRV), cardiac pre-ejection period (PEP), and respiration rate and depth were measured via impedance cardiography. Veterans with PTSD symptoms displayed reduced lnHF-HRV, even when adjusting for respiration, but their partners did not. In mediational analyses, elevated resting HR in PTSD was accounted for by lnHF-HRV but not PEP. Results strengthen evidence regarding HF-HRV and elevated HR in PTSD.