From the Database Blocking Tree window you can expand the tree of a blocking session to see the sessions it is blocking.

From the Database Sessions window, you can view:

• Session ID: the Session ID of the sessions causing the block, and the sessions being blocked
• Client: the names of the machines where the session is blocked
• User: the user of the blocked session
• Query: the query that is blocked or causing the block
• Blocked Object: the object that is blocked
• First occurrence of block: the time that the block first occurred in the specified time range
• Block Duration: the amount of time that the session was blocked or causing the block