Crystal Heart

The "Crystal Heart" is located at the center of the Crystal Temple, and was first seen in "Together Breakfast", and last seen in "Secret Team"

About
The Crystal Heart resembles a huge, red, crystal structure, and Pearl stated that it's connected to the most dangerous parts of the temple. The central vein connected to the bottom of the Heart leads directly down into The Burning Room, via Rose's Room.

"Together Breakfast"
Steven gripped onto one of the blood vessel tubes, and then slid down it while seeing into other rooms.

"Secret Team"
Amethyst and Steven attacked the escaped arms on its vessels.

Trivia

 * When Steven slides down the center vein, the middle area is Rose's Room, hinted by the primary tune played in the episode "Rose's Room" and because of the pink clouds shown.
 * Smaller seemingly organic hearts that may be similar to the crystal heart can be seen inside the Injectors in "On the Run."
 * It is rumored that the temple is a giant Gem and the crystal heart could be its heart.
 * Another possibility is that the Temple looks like all the Crystal Gems Fused together.
 * The Kindergarten Control Room (from "Marble Madness") and Gem Warship seem to have their own versions of the Crystal Heart.
 * In both cases, the places were destroyed when their "heart" was damaged. It is possible this is the reason why Pearl alerted Steven that the Crystal Heart is connected to the most dangerous places of the Temple.
 * Another similarity is that the main power source connects all the parts of the body by energy tubes (vessels).

Crystal Heart