# TestRequest (35=1)

`Heartbeat (35=0)` and `TestRequest (35=1)` messages are used by NDAX to monitor the live status of a FIX Session.

The Heartbeat message `(tag 35=0)` and the TestRequest message `(tag 35=1)` are used by the National Digital Asset Exchange (NDAX) to monitor the live status of a Financial Information eXchange (FIX) session. In the event that no response is received within the agreed-upon heartbeat interval, as specified by the HeartBtInt field `(tag 108)` in the Logon message `(tag 35=A)`, NDAX will send a TestRequest message to the client. The client must respond immediately to the TestRequest message to confirm that the FIX session is still active. 

If NDAX does not receive a response to the TestRequest message within the heartbeat interval, it will terminate the FIX session to the counterparty. The Heartbeat and TestRequest messages are important tools for ensuring the reliability and continuity of the FIX session, and help to ensure that the connection between the client and NDAX is functioning properly.

<table><thead><tr><th width="80">Tag</th><th width="130">Field Name</th><th width="123">Data Type</th><th width="78">Req’d</th><th>Description</th></tr></thead><tbody><tr><td>112</td><td>TestReqID</td><td>String</td><td>Y</td><td><code>TestRequest (35=1)</code> identifier.</td></tr></tbody></table>


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