Q: what has more of an impact on your bmr, your lean body mass or your cardiovascular health?

A: I wouldn't say that your cardio health directly impacts your BMR the way that your lean body mass does. But at the same time, don't underestimate the importance of cardio health either. Besides the well-known health benefits, a well-developed cardio system will allow you to recover quicker in between weight lifting sets allowing more intense workouts. It's certainly a mistake to ignore your cardiovascular health just because it does not directly impact BMR.