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# Algorand Specifications

The _heartbeat_ is a special transaction used to challenge the liveness of an _online_ account.

A _heartbeat_ transaction additionally has the following fields:

| FIELD | CODEC | TYPE | REQUIRED |
| --- | --- | --- | --- |
| Heartbeat Address | `a` | `address` | Yes |
| Heartbeat Seed | `sd` | `[32]bytes` | Yes |
| Heartbeat Vote ID | `vid` | `[32]bytes` | Yes |
| Heartbeat Key Dilution | `kd` | `uint64` | Yes |
| Heartbeat Proof | `prf` | `struct` | Yes |

The _heartbeat address_ is an account address that this heartbeat transaction proves liveness for.

The _heartbeat seed_ is a block seed.

- It **MUST** be the block seed found in the _first valid round_ of the transaction.

The _heartbeat vote id_ is a public key.

- It **MUST** be the current public key of the root voting key of the _heartbeat_ address’s account state.

The _heartbeat key dilution_ is a key dilution parameter (see [Algorand Participation Keys specification](https://specs.algorand.co/keys/keys-ephemeral)).

- It **MUST** be the current key dilution of the _heartbeat address_’s account state.

The _heartbeat proof_ **MUST** contain a valid signing of the _heartbeat seed_ using the _heartbeat vote id_ and the _heartbeat key dilution_ using the voting signature scheme defined in the [Algorand Participation Keys specification](https://specs.algorand.co/keys/keys-participation).

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