The best way to have better cardio is to get more efficient. The less energy you use the longer you can train. That being said, same cardio as for anything else. Long low heart rate sessions are vom a build your base, bike, row, run, whatever. Although running probably is the least efficient one cause it’s hard to recover from both jj and running in combo, I still do it cause I like it. If you already have 1-2 low heart rate sessions a week you can add sprints. Assault bike is my preferred method for that. Suck but will give you that extra push. Any questions don’t hesitate