A wearable medical monitoring (WMM) system may be worn for a long time. Some embodiments of WMM systems are wearable cardioverter defibrillator (WCD) systems. In such systems, ECG electrodes sense an ECG signal of the patient, and store it over the long-term. The stored ECG signal can be analyzed for helping long-term heart rate monitoring of the patient. The heart rate monitoring can be assisted a) by special filtering techniques that remove short-term variations inherent in patients' short-term heart rate determinations, and b) by indication techniques that indicate when conditions hampered sensing of the ECG signal too much for a reliable heart rate determination.