Ever done a set of six heavy squats? Sprinted up a hill? The heart-pounding, leg burning, lung heaving results are almost identical. Strength and cardio don't really exist - they're at opposite ends of an intensity spectrum. Sure, you can walk and not really build your strength, or you can do isolated biceps curls and not really stimulate much of a cardiovascular response, but...
Here's pretty much what it comes down to: if you want to develop strength and skills, full-body practical strength, train full-body movements at intensity. Rest for a generous while, then repeat until you're satisfied. If you want to develop your cardiovascular capacity, do the same things, with the shortest rest periods you can manage. That's all. It only comes down to rest periods. There's no reason why you should rest for a while or a moment - beyond what you feel like.
Afterwards, you can always isolate a weaker muscle group, do some postural work, stretch, or go for a walk or a jog if you feel like your workout didn't quite capture what you were after. That's the role for isolation work in my book - after your main things, to bring up your weak points. And cardio too, if you haven't quite satisfied yourself, you can always go for a little jog or something.
But this strength vs. cardio thing - I just don't buy it any more. Your body doesn't categorise - it knows work and rest, intensity and duration, but it doesn't care at all about our concepts for exercise.