Abstract Our previous study demonstrated a contribution of the paraventricular nucleus of hypothalamus (PVN) in processing of carotid body (CB) chemoreflex. Nitric oxide (NO) (within the PVN) known to modulate autonomic function is altered in rats with HF. Therefore, the goal of the present study was to examine the influence of endogenous and exogenous NO within the PVN on the sympathoexcitatory component of the peripheral chemoreflex in normal and heart failure (HF) states. We measured mean arterial blood pressure (MAP), heart rate (HR), renal sympathetic activity (RSNA), and phrenic nerve activity (PNA) in Sham operated and HF rats (6-8 weeks after coronary artery ligation) after incremental doses of potassium cyanide (KCN; 25-100µg/kg; i.v.). There was potentiation of the reflex responses in HF compared to Sham. Bilateral microinjection of an inhibitor of NO synthase, N(G)-monomethyl-L-arginine (L-NMMA; 50 pmol) into the PVN augmented the RSNA and PNA response to peripheral chemoreceptor stimulation in Sham rats, but had no effect in HF rats. Conversely, bilateral microinjection of a NO donor, sodium nitroprusside (SNP; 50 nmol) into the PVN attenuated the RSNA response of the peripheral chemoreflex in Sham rats but to a smaller extent in HF rats. These data indicate that; 1) NO within the PVN plays an important role in processing of CB chemoreflex and 2) there is an impairment of the NO function within the PVN of HF rats, which contributes to an augmented peripheral chemoreflex and subsequent elevation of sympathetic activity in HF.