GIMP Version: 2.8.10
Operating System: Windows
GIMP Experience: Beginner Level

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I want to convert an image of a human heart metal heart

Do you mean something like this.

That would make an excellent "steam punk" project!

First of all, after opening your image, right click the layer in the layers dialogue, then click add alpha channel. Click (color select tool) and select the black background. then go to selection and click grow 1, then click delete. That should have removed the black background.
You will now have your organs on a transparent background (checkerboard).

Right click on your layer and click alpha to selection, that will put the marching ants around your images.
Go to filters, alpha to logo, then click Bevel Reflect Logo, The dialog will come up and I left it all at default except on the top, I chose round bevel and for the spherical emap I chose one of my gold emaps.
Click OK

There are a lot of emaps you can download from here and I will post them or direct you to the thread where they are.
Place you emaps in in a folder and name it
Place the Bevel Reflect.scm in your user name Scripts folder.
Any questions, please post back here and someone will help.

ML Bevel Reflect goes into your Plug-ins folder
Environment Map sharing thread... viewtopic.php?f=12&t=9677&start=140

Way too small to do right. Anyway, used some metallic curves (click here) and also some things for cleanup mainly.