You know the feeling when you've not been paying that much attention to your cardio and now you need to get it back. Before you do something punishing like The Wrath of Odin you may first try something that is just a tad corrective, like the Corrector workout. Gentle on your lungs (though it may not feel that way) and your cardiovascular system (that gets oxygen from your lungs to your muscles) it is also a great way to simply maintain your aerobic fitness when you're just not training very hard. Add EC. You know you just have to.
Extra Credit: 1 minute rest between sets.