Rudra Hridaya Upanishad is one of the 50 Upanishads of YajurVeda. Here you can download the PDF document of Rudra Hridaya Upanishad.
This Upanishad explains the significance of Rudra Hridaya, the sacred heart of Rudra, the Aatma, Antaratma, and Paramatma of the universe.
It also details the importance of Trimurti and their tathwa. To rule the universe peacefully, Rudra is incarnated as Shiva, Vishnu, and Brahma.
Rudra Hrudaya Upanishad is a conversation of Sukha and his father Sage Vyasa. Vyasa clarifies all the doubts of his son Sukha regarding the Rudra.