Crystal Heart

The "Crystal Heart" is located at the center of the Crystal Temple. It was first seen in the episode "Together Breakfast", and most recently seen in the episode "Catch and Release".

About
The Crystal Heart resembles a huge, red, crystal structure. Pearl stated that it is 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. Due to the rhythmic beating and vein-like apparatuses, the crystal heart gives the Crystal Temple a sense of being alive.

"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.

"Catch and Release"
Steven rides the central vein from Rose's Room into the Burning Room in order to question Peridot about her behavior at the Galaxy Warp.

Trivia

 * The Crystal Heart very literally connects to all known Crystal Gem rooms- Amethyst and Pearl's rooms are connected via corridors on the main floor. The vein beneath the heart goes through Rose's room (Seen within the room in Catch and Release.), and leads directly to the Burning Room.
 * When Steven slides down the center artery, the middle area is Rose's Room, hinted by the primary tune played in the episode "Rose's Room" and its overall cloudy appearance.
 * Smaller, seemingly organic hearts that may be similar to the Crystal Heart can be seen inside the Injectors in the episode "On the Run".
 * The Kindergarten Control Room 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 the energy tubes that provide power for the structure.