Heart Rate Training

To build my base cardio, the last two runs I've done have been heart rate training. Specifically, I ignored my time and pace, and instead focused on keeping my heart rate in zone 3. For me this was about 150 bpm. I was actually a bit surprised that doing this made the run much more enjoyable. I didn't come back and feel utterly exhausted or feel like I might pass out. I think I may have been pushing too hard in general these last few years instead of building the solid base.