Sodium azide (NaN₃), a potent vasodilator, causes severe hypotension upon accidental exposure. Although NaN₃ has been shown to increase coronary blood flow, the direct effect of NaN₃ on coronary resistance vessels and the mechanism of the NaN₃-induced response remain to be established. To address these issues without confounding influences from systemic parameters, subepicardial coronary arterioles were isolated from porcine hearts for in vitro study. Arterioles developed basal tone at 60 cmH₂O intraluminal pressure and dilated acutely, in a concentration-dependent manner, to NaN₃ (0.1 µM to 50 µM). The NaN₃ response was not altered by a nitric oxide synthase inhibitor (L-NAME) or endothelial removal. Neither inhibition of phosphoinositide 3-kinase and tyrosine kinases nor blockade of ATP-sensitive, calcium-activated and voltage-dependent K⁺ channels affected NaN₃-induced dilation. However, the vasomotor action of NaN₃ was significantly attenuated in a similar manner by the inward rectifier K⁺ (K_ir) channel inhibitor (Ba²⁺), the Na⁺-K⁺ ATPase inhibitor (ouabain), or the guanylyl cyclase inhibitor (ODQ). Ba²⁺ in combination with either ouabain or ODQ nearly abolished the vasodilatory response. However, there was no additive inhibition by combining ouabain and ODQ. The NaN₃-mediated vasodilation was also attenuated by morin, an inhibitor of phosphatidylinositolphosphate (PIP) kinase, which can regulate K_ir channel activity. Using whole-cell patch-clamp methods, NaN₃ acutely enhanced Ba²⁺-sensitive K_ir current in isolated coronary arteriolar smooth muscle cells. Collectively, this study demonstrates that NaN₃, at clinically toxic concentrations, dilates coronary resistance vessels via activation of both K_ir channels and guanylyl cyclase/Na⁺-K⁺ ATPase in the vascular smooth muscle. The K_ir channels appear to be modulated by PIP kinase.