work in HIIT into your workout
sprint for some distance (~50 - 80m), wait 30 seconds, turn around and do it again
this works your anaerobic and aerobic systems and will help improve cardiovascular function
this is what I've been doing and awhile ago i made a similar topic and a lot of people bashed me for not being able to run I think a 5k in under 21 25 minutes but after training I ran a 5k in 17 minutes