Zatch Bell! - S1E135

Faudo: Deadly Zone. The Demon That Beats the Heart. Momon's Tears.

The team consisting of Kiyo, Zatch, Sunbeam, Ponygon, Elle, and Momon, continues through the blood vessel maze and end up in a room where many different paths present themselves. They follow Momon's directions and end up at Faudo's heart. Faudo's guardian of the heart reveals a room in the spinal cord that will give them a detailed map of Faudo's body.