What is dyspnea and cardiac dythesia?

Dyspnea is difficulty breathing... for what ever reason. I assume you mean Cardiac Dyspnea rather then "Dythesia" (no such word) Cardiac Dyspnea is difficulty breathing due to cardiac (heart) origins. This is usually known as Pulmonary Edema which is kind of like "lung swelling." Usually the heart becomes damaged or enlarged and becomes a much less efficient pump. Then there is a backup of blood in the lungs because the left ventricle, the main pumping chamber of the heart, is dysfunctional usually below 20% of full function. Another scenario is that you have ingested to much fluid or to much salt and retained to much fluid for the failing heart to function. ( I have seen Congestive Heart Failure patients eat a well endowed dill pickle during dinner, and be in the hospital ER by 3-4 AM.) This blood back up begins to push the blood plasma (liquid part of the blood) out of the billions of vessels in the lung and into the billions of microscopic air spaces (avieoli) and the breathing function becomes more and more difficult, as respiration (exchange of gases O2 and CO2) begins to fail. You are essentially drowning in your own fluids. It is a life threatening situation, and requires at least a well trained Paramedical team to administer the needed medications that will extract the unnecessary fluid from the body, (as urine) reducing the episode to a much more manageable situation. This usually requires a few days in the hospital until your fluid levels are optomized by medicine usually, and your considered stable.

Dyspnea means difficulty breathing.
Dys = difficulty
Pnea = breathing

I have never heard of cardiac dythesia.