This was a solid long run: 16.3 km in nearly two hours, completed at a fluid easy pace with normal legs and no discomfort.
The growing mileage is starting to feel present, which is expected at this point in the marathon block. The important signal is that the effort stayed controlled and the run finished without pain or a major fade.
The heart rate peak near 184 bpm does not match the surrounding pace pattern and then dropped abruptly at similar effort. It is more likely a temporary wrist-sensor reading issue than a real sustained intensity spike.
Takeaway. The aerobic base is building well. Keep long runs fluid and conversational, then use threshold workouts to develop the ability to sustain faster pace without turning every quality session into a race.
Next step. W04D2 Intervals. Three longer threshold repetitions to build sustained strength. Progress gradually through the workout and finish controlled rather than heroic.