The speaker begins by arguing with themselves. The heart is just an organ, they say, and treating it as a feeling thing is a lie. But poetry doesn't need truth, so the poem goes on to do exactly that: the heart speaks, the skin dreams, and the body becomes the place where a past relationship still lives.
What the speaker feels is longing mixed with grief. Remembering time spent with someone sends "harmonic shivers" up the spine, a phrase that makes the feeling sound both musical and physical. The fingertips hold memories of touch, and the liver is "in mourning," an odd, almost darkly funny choice that shows how far the sadness has spread through the body. The veins keep flowing, as if life carries on regardless.
The mood is intimate, wistful and a little sensual. The scattered line breaks near the end, with the spine shivering again, make the poem feel like a memory that keeps returning.