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# HKHeartbeatSeriesSample

A sample that represents a series of heartbeats.

```
class HKHeartbeatSeriesSample
```

## Overview

Use a [`HKHeartbeatSeriesQuery`](/documentation/HealthKit/HKHeartbeatSeriesQuery) to access the underlying heartbeat data.

The [`HKHeartbeatSeriesSample`](/documentation/HealthKit/HKHeartbeatSeriesSample) class is a subclass of the [`HKSeriesSample`](/documentation/HealthKit/HKSeriesSample) class. These samples are immutable; you set the sample’s properties when you build them, and they can’t change.

### Extend Heartbeat Samples

Like many HealthKit classes, you shouldn’t subclass the [`HKHeartbeatSeriesSample`](/documentation/HealthKit/HKHeartbeatSeriesSample) class. You may extend this class by adding metadata with custom keys to save related data used by your app.

For more information, see [`addMetadata(_:completion:)`](/documentation/HealthKit/HKHeartbeatSeriesBuilder/addMetadata(_:completion:)).

## Topics

### Metadata

[`HKMetadataKeyAlgorithmVersion`](/documentation/HealthKit/HKMetadataKeyAlgorithmVersion)

A key that indicates the version number of the algorithm used to calculate the sample’s value.


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