To add to the scale comment, just remember that the more excess you have, the more you have to drag along, so although the scale may not indicate your fitness level, your weight will still have an effect on your cardio.
As a side note, if you're looking to improve your cardio, as in VO2 max, try HIIT training. It consist of alternating in between long intervals of High Intensity Training and short intervals of rest/low intensity training.
IE, walk at a 3.0-3.5 miles/h pace for 1 min, then run at a 8.5-9.0 miles/h for 1-2 min, alternate while slowly increasing your running time.
On the weights side, building endurance and strength, combine antagonist movements in super sets and take about 30-45 sec in between sets.
IE, set of 10-12 reps on the bicep curls then immediately run over to a set of 10-12 reps on the skullcrushers or triceps push downs, then take a 30-45 sec break, then repeat for a total of 4 sets, switch to another exercise in the same muscle groups and repeat.
I guarantee after you will feel it after every work out and you will notice a improvement in all fields within a few weeks. I guarantee you will want to puke the first few times you do it, you just have to push yourself through it and keep on your times (you can cheat a little at first to get used to the intensity).
Another concept to develop both VO2max and Strength/Endurance is the DTP program, made famous by bodybuilding.com chief editor Kris Gethin. This program consist of doing a workout with only 1 compound exercise (aka bench press, full squats, deadlifts, basically an exercise which works multiple muscle groups) and doing pyramid sets of 50-30-15-8-4-8-15-30-50 (somewhere along that range) with minimal rest in between the sets and increasing your weights for each set, so that when you get to your 4 set you should be around your maximum weight capabilities, then you pyramid down the weights until you get to your 50 reps again. This training is a little more advance but i guarantee you will ache in areas you never knew you had muscles.
As for me, i currently follow something a little more oriented towards building size as I was way underweight (sitting around 105 lbs at 5.8, now at 170 after 2 years), which is basically a HIIT training on the cardio and a Pyramid program on the weights with target training (focussing on 1 muscle group per workout) and going as heavy as i can on the weights.
I suggest taking a look at this website, contains allot of good workout programs, from beginner to advance, it has everything. Most of them are written by professional trainers or bodybuilders and the best part is that its free.
http://www.bodybuilding.com/fun/workout.htm
my :2c: