Handling Distributed Transactions in ADO.NET
The Pool Manager groups the connections according to the requirement for transactions. If the requesting thread requires a specific transaction context, it must be matched to a connection with the same transaction context, for example, a connection that has been enlisted in distributed transactions.
Because closed connections are returned to the appropriate connection pool, you can close a connection even though a distributed transaction is pending. This means that you can still commit or rollback the distributed transaction until the connection is closed at the server.