---
updatedAt: 2026-09-29T18:07:14.000Z
agentTools:
  projectIndex: https://docs.zerohash.com/llms.txt
---

# Heartbeat (35=0)

Heartbeats for FIX on the zerohash CLOB.

This section indicates the message intended to monitor the status of the communications link during periods of inactivity.<br />The FIX market data accepts and generates Heartbeat messages as per the FIX specification.

* **Inbound:** Handled as specified
* **Outbound:** In response to a test request or timeout.
* **Response:** None

The heartbeat message should be sent if agreed upon Heartbeatinterval has elapsed since the last message sent, which is `60` seconds by default.

| Tag | Field Name   | Required | Note                                                                                                                   |
| --- | ------------ | -------- | ---------------------------------------------------------------------------------------------------------------------- |
| 8   | BeginString  | Yes      | Must be set to FIXT.1.1                                                                                                |
| 9   | BodyLength   | Yes      | Message length in bytes up to the checksum field                                                                       |
| 35  | MsgType      | Yes      | Must be set to 0 (Heartbeat)                                                                                           |
| 49  | SenderCompID | Yes      | Provided by zerohash                                                                                                   |
| 56  | TargetCompID | Yes      | Static value for all sessions. `ZERO`                                                                                  |
| 34  | MsgSeqNum    | Yes      | Monotonically increasing sequence number.                                                                              |
| 52  | SendingTime  | Yes      | UTC time that the order was sent down to nanosecond resolution.                                                        |
| 10  | CheckSum     | Yes      | Three byte checksum calculated by summing every byte in the message up to and not including the checksum field itself. |

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