"No Cardio? How do you train your heart?"
The heart serves the needs of all life sustaining organs and the muscular system. It is the demands placed upon the muscular system that determines how hard the cardiorespiratory system is working. Your heart does not know if you are doing yoga, running up a hill, or performing a set of squats. Muscular effort is mechanical work, and mechanical work is the passkey to all of your metabolic machinery. There is no such thing as "cardio" exercise; all exercise (mechanical work) of adequate intensity is "cardio." In reality, low intensity "Cardio," the way most people perform it, is an introductory form of exercise; it is beneficial for the severely de-conditioned, the elderly, or those who want to kill some time. Plodding along on a treadmill, or sitting on a lifecycle while watching "Ellen" is not an effective use of time.
"Well, what about fat loss?"
Low intensity cyclic activities (treadmill, elliptical, etc...) do not require much mechanical work, so they do not burn a lot of energy. To maximize fat loss, you must burn as much fuel as rapidly as possible; the higher the effort and greater the range of motion, the greater the fat burning effects.
"Well, I plan on running a 5k, I like to train on a treadmill when it rains"
In order to make improvement in any sporting activity, you must perform that specific activity as it is performed on game day. Any improvements achieved on a treadmill WILL NOT transfer to running on solid ground. If you compete in an endurance sport, perform your specific activity (cycling, running, etc...) in order to improve performance.
If your goal is to look good and cultivate health, perform moderate to high intensity mechanical work, such as sprints, circuit training, or bodybuilding type training. When properly implemented, this type of training will build muscle, improve joint function, and maximize fat loss. So get off of the hamster wheel and partake in activities that make you DO MORE WORK.