This study investigates whether the electrocardiogram (ECG) signal of pilots shows responsiveness towards unexpected events in highly dynamic environments. These event-related heart rate (HR) responses are manifestations of arousal and might indicate the beginning of a high-workload phase. For the collection of HR response data, we conducted an experiment in a fast-jet simulator with eleven participants using a three-lead ECG sensor. The participants had a high degree of motivation and prior experience with flight simulators. The experiment consisted of six experiment blocks with varying difficulties. To trigger arousal, we included six types of events. After the experiment, we computed differences in the HR and heart rate variability (HRV) for the pre- and post-exposure to each event. The results show that the response is highly dependent on the type of event and the individual. It appears that both ∆HR and ∆SD1/SD2 may be indicative of arousal. However, given that the flight missions set in a naturalistic environment, it is not possible to ensure that mental workload did not affect responses. Results also indicate that HR and HRV alone are not reliable precursors to the onset of a workload phase. Someone must take the task context into account. Nevertheless, HR-related responses appear to be valuable features for the capture of coping mechanisms and can be used in an early operating adaptive assistance system. The underlying objective of this research is the development of an adaptive assistance system in the field of Manned-Unmanned Teaming (MUM-T) missions.