> ## Documentation Index
> Fetch the complete documentation index at: https://docs.kraken.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Heartbeat

> Keep the session alive during inactivity

<div className="api-banner">
  <span className="api-protocol fix">FIX</span>
  <span className="api-detail">session: admin</span>
  <span className="api-tag">35=0</span>
</div>

Sent when no other traffic has passed within the negotiated heartbeat interval, so that both sides can tell a quiet session from a dead one. When it answers a Test Request it must echo that request's TestReqID. The interval is negotiated through HeartBtInt (108) on Logon.

**Direction:** Either direction

***

<ResponseField name="header" type="" required>35=`0`</ResponseField>

<ResponseField name="112 - TestReqID" type="string">
  Token identifying the test request. A heartbeat answering a test request must echo the value it carried.

  <span className="field-attr">Required:</span> Conditional
</ResponseField>

<ResponseField name="trailer" type="" required />