Day 3 Marathon Training. Well that sucked...

I have such a low and slowly rising heart rate that its making it almost impossible to run 4 minutes in zone 4. In my 90 seconds recovery, my HR drops so much it takes 1/2 of the run to get it back up to zone 4. Im so disappointed in this workout today I may go out and run sprints tomorrow even though I am not scheduled to run. https://www.strava.com/activities/5208688872