This is a photomicrograph I had taken about eight or ten years ago when I was examining some sections of mouse arterioles. As it so happens, it was Valentine’s day when I took this, so I saved the image just because of the resemblance. Naturally, real blood vessels are round(ish) in cross-section, so the shape is obviously an artefact of fixing or sectioning. Nevertheless, I thought the coincidence was noteworthy.
Happy Valentine’s Day!