There are a lot of people who can become confused with the various terms that are available. If you would check cardiac dysrhythmia and cardiac arrhythmia, you would see that they both refer to having an irregular heartbeat that some people seem to have.
The main difference is what they particularly refer to. When you say dysrhythmia, this means that the rhythm of the heart is a bit abnormal. When you are dysrhythmia, this means that there is no rhythm at all. There are times when the abnormalities will happen depending on the state of the heart.
For example, someone may have an irregular heartbeat depending on the pace of the exercise that he is doing.