Hello and welcome to HCM. I carefully read your question and I understand your concern. But don t worry, we will deal with it and Ill try to give you some advises. If you tell me that your girlfriend rhythm is regular but with a frequency over 100 beat for minute, my opinion as cardiologist is that we are talking about a simple sinus tachycardia. Normal heard beat should be between 60-100 beat for minute, but this of course changes in different people and secondary to physical activity.The maximal heart rate for a 37 years old should be 183 beat for minute. So, if you tell me that her resting heart beat is up to 100 we should understand why. There are a lot of reasons causing sinus tachycardia. If I was your treating doctor I will recomend you some examinations like: -simple blood analyze. Sometime a simple anemia can cause tachycardia -thyroid Hormones, Because excessive thyroid hormones, hyperthyroidism can cause tachycardia. - I will recommend a holter monitoring to verify and see the rhythm tendency during the day an echo cardigraphy. At mean time she should avoid Coffey and cafe-in products because they rise heart frequency. All these for a simple chek up. Hope I was helpful. Best regards