Summary Objective The authors investigated the potential effectiveness of biofeedback as a complementary treatment for PTSD. Design This exploratory study used heart variability biofeedback and determined its efficacy in treating PTSD through the use of two rating instruments, The Post-traumatic Stress Disorder Checklist (PCL)-Military version and the Zung Self-Rating Depression Scale. Active duty service members deployed to Iraq or Afghanistan were alternatively assigned to a treatment as usual control group and treatment as usual with the addition of biofeedback. The authors administered the two instruments before treatment and at the conclusion of three weeks of biofeedback therapy. Results Biofeedback did not produce a measurable improvement. A one way repeated measures analysis of variance (ANOVA) was used to examine change in PCL scores over time. There was a main effect for time, F(1, 36)=11.98, p <.001, indicating a decrease in PCL scores from baseline to three weeks for both the control and treatment group. Results demonstrated a nonsignificant main effect of group, F(1, 36)=.1.79, p =ns, and a nonsignificant group by time interaction, F(1, 36)=.2.59, p =ns. Similarly, for depression, results showed a significant main effect for time, F(1, 33)=10.26, p <.003, indicating a decrease in Zung scores from baseline to three weeks for both the control and treatment group. Results demonstrated a nonsignificant main effect of group, F(1, 33)=.385, p =ns, and a nonsignificant group by time interaction, F(1, 33)=3.52, p =ns. Conclusion The addition of biofeedback did not produce a measurable improvement in PTSD or depression scores in this exploratory study.