EYE OPENER

Though this might not be what you see on a typical Valentine's Day card, it is what the human heart actually looks like.

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Have a little heart
FRANKFURT, GERMANY

Well... what it looks like very close-up.

What you're actually seeing are the actin-based protein structures within cells that form sarcomeres – the structures responsible for making your heart beat. These structures are woven with highly interconnected mitochondrial networks (seen here in blue) that are crucial for the heart's energy supply.

These sarcomeres are particularly special as they're made from human induced pluripotent stem (iPS) cells. "Heart cells can't regenerate after damage," says Dr Till Stephan, a German cell biologist at Goethe University in Frankfurt, who took this award-winning picture. "So cardiomyocytes [heart cells] derived from iPS cells may one day be routinely used to repair heart injuries."

Stephan took this photo using microscopy, which he describes as "a vital tool in life sciences". Microscopy allows researchers to study individual cells at a subcellular level, unveiling the complexity of structures and processes within them.