code: func (cli *OpsGenieClient) Heartbeat() (*OpsGenieHeartbeatClient, error) {
  	cli.makeHTTPTransportSettings()
  
  	heartbeatClient := new(OpsGenieHeartbeatClient)
  	heartbeatClient.SetOpsGenieClient(*cli)
  
  	if cli.opsGenieAPIURL == "" {
  		heartbeatClient.SetOpsGenieAPIUrl(endpointURL)
  	}
  
  	return heartbeatClient, nil
  }
docs: // Heartbeat instantiates a new OpsGenieHeartbeatClient.