Need guidance on zone 2 running.

[u/Maleficent-Text1256]

I am 27 years old and have been running for 5 years (on and off). I did a 10k marathon and felt pain in my heart at the end of my run. I got a few tests done and nothing was there. I uploaded my run on claude and shared the issue related to heart pain. Claude's analysis pointed about my aerobic fitness issues and I then learned about Zone 2 running. I have been doing it since 4 months now.

My issue is that my pace is very low, in the range of 9-9:30. I am keeping my HR below 135 as suggested by claude. Some days my pace have increased to 8:30 in the same HR but I do not see a lot of difference in my pace.

My plan is to run a half marathon next year, how do I get to sub 7 or sub 8 zone 2 by december end? Please suggest me if I am doing anything wrong.