This is the actual error raised when heartbeatFrequencyMS is less than 500:

>>> MongoClient(heartbeatFrequencyMS=499)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "pymongo/mongo_client.py", line 538, in _init_
heartbeat_frequency=options.heartbeat_frequency)
File "pymongo/settings.py", line 46, in _init_
common.MIN_HEARTBEAT_INTERVAL * 1000)
pymongo.errors.ConfigurationError: heartbeatFrequencyMS cannot be less than 0heartbeatFrequencyMS cannot be less than 0heartbeatFrequencyMS cannot be less than 0heartbeatFrequencyMS cannot be less than 0heartbeatFrequencyMS cannot be less than 0heartbeatFrequencyMS cannot be less than 0heartbeatFrequencyMS cannot be less than
....
0heartbeatFrequencyMS cannot be less than 0heartbeatFrequencyMS cannot be less than 0heartbeatFrequencyMS cannot be less than 0heartbeatFrequencyMS cannot be less than 0heartbeatFrequencyMS cannot be less than 0heartbeatFrequencyMS cannot be less than 0heartbeatFrequencyMS cannot be less than 0