The Grove Ear-clip Heart Rate Sensor, is an ear-clip with an accompanying receiver, which can be used to measure the pulse.

Further information to the sensor you will find here.
Ear-clip Heart Rate Sensor can be ordered here.

When the pulse beats, an increased voltage is measured via pin C16. This can be found under the "Advanced" blocks under "Pins > ... more" with the block "if pin P0 pulsed high". You only have to select the correct pin, which in this case is C16, and it is possible, for example, to have an LED light up simultaneously with the pulse. If the pulse is low and therefore on "low", the LED can be switched off again via the same block.

In Open Roberta Lab there is no direct query whether the measured voltage is currently high or low. To measure the heartbeat the digital value of the configured pin C16 must be queried. If the value is 1, a heartbeat is measured. If the value is 0, none is measured.