A wearable medical device is defined, the device comprising:a water-resistant harness to be worn by a patient；a plurality of ECG sensing electrodes disposed on the harness and configured to sense an ECG of the patient；a plurality of therapy electrodes discrete from the plurality of ECG sensing electrodes, the plurality of therapy electrodes also disposed on the harness and configured to provide at least one defibrillating shock to the body of the patient； anda control unit, electrically coupled to the plurality of ECG sensing electrodes and the plurality of therapy electrodes, configured to monitor the sensed ECG of the patient, and responsive to detection of cardiac arrhythmia of the patient, to provide at least one defibrillating pulse of energy to at least one of the plurality of therapy electrodes, the control unit being housed in a waterproof case formed from a waterproof material that is sealed to prevent ingress of water during operation of the wearable medical device in a wet environment.
