Heart shaped rock art

Here are 2 examples of heart portable rock art. The obvious scenario of how they were able to carve these pieces anatomically correct is quite gruesome. The question is why?

It is well documented that some early cultures ritually defleshed the dead. Discarding the flesh and then after the bone was subject to the air for a wile they were anatomically arranged in a fetal position laying on the right side for burial. Its not a stretch to assume they would be very knowledgeable about human anatomy. As to why they made yhem that is a great mystery. JP