Your terminology is correct and is defined as a slow heart beat, not an irregular heart beat. The normal heart rate for a medium size dog is 80-120 beats per minute. Bradycardia is anything less than 80 beats in a minute in dogs. Heart rate is dynamic and changes with sleep, exercise, and even simple breathing. So, first find out how slow your dogs heart rate is and this will give you an idea of how drastic the bradycardia actually is. Second, keep your eye on her and look for the symptoms: lethargy (tired) or difficulty breathing. It is only when the slow heart rate is actually decreasing the dogs quality of life or health that it should become a concern. Keep in mind, many athletes (generally professionals) have low heart rates. She could live with a low heart rate for many years to come.