Heart rate must be obtained from ECG signals. The "heart rate" obtained from PPG is generated by the change of the light absorption rate of superficial blood vessels. Strictly speaking, this “heart rate” is pulse rate, not the "heart rate". Heart rate characterizes the frequency of periodic heart activity, while pulse rate characterizes the frequency of pulse periodic activity. Usually, heart rate and pulse rate are equal, but for some serious cardiovascular diseases, such as atrial fibrillation, the heart rate is much greater than the pulse rate. Therefore, for general consumer electronics applications, because the requirements are not so strict, we generally do not make a strict distinction between heart rate and pulse rate. At this time, it is the same to choose ECG signals and optical signals, so users can choose ECG sensors or optical sensors. Maxim also has the only sensor in the market that supports both ECG and optical measurements, MAX86150. Among medical instruments which must meet much more strict standards, heart rate must be obtained from ECG signals, and ECG sensors can be only selected at this time.