How Nitric Oxide Works

Normal Endothelial dysfunction With PDE5 inhibitor

cGMP level

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of maximum

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Quick guidance

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Hover the cGMP bar or the vessel for quick tip. Changes update the legend and are announced.

How to read this animation

The left panel releases tiny NO particles that travel rightward. They represent nitric oxide released by nerves and endothelium during arousal. When many particles arrive, the middle sGC icon brightens, signaling enzyme activation that makes cGMP.

The tall bar at the right is the intracellular cGMP pool. As sGC activates, the blue-green fill rises. A higher fill means stronger smooth-muscle relaxation and wider blood channels. The bottom vessel (the corpus cavernosum) expands and narrows visually as the cGMP level changes — the vessel is shown in red to highlight engorgement.

The small PDE5 scissor stands for the enzyme that breaks down cGMP. In the “With PDE5 inhibitor” state, the scissor fades and the cGMP pool stays high. In “Endothelial dysfunction,” fewer NO particles reach sGC, sGC stays dim, cGMP stays low, and the vessel remains narrow.