This is Melotte 15, an Open Cluster in the constellation of Cassiopeia, probably better known as "The Heart of the Heart"; it is the centre cluster of stars within The Heart Nebula, IC1805 (also known as Sharpless 2-190). Melotte 15 is about 7,500 light years away from Earth.
When photographed under visible wavelength, the nebula's intense red colour and its configuration are driven by the Hydrogen Alpha radiation emanating from a small group of stars near the nebula's centre. This open cluster of stars, known as Melotte 15, contains a few bright stars nearly 50 times the mass of our Sun, and many more dim stars that are only a fraction of our Sun's mass. The grouping is only about 1.5 million years old and its lifespan is expected to be as short as 3-6 million years.
This image was created by adopting the Hubble false-colour palette for mapping narrowband emissions from Sulphur, Hydrogen Alpha and Oxygen atoms to the red, green and blue channels respectively. So, the cyan/blue colours are the intense reds (Hydrogen Alpha) that you would normally see when photographed under visible wavelength, with the yellow/orange colours representing the Sulphur.
Imaged over two nights, with just over 6 hours of total integration time.
25x5mins Ha, 25x5mins Sii, 25x5mins Oiii, plus Darks Flats and Flat Darks. Stacked and processed in PixInsight, with final colour balancing in Photoshop.