Tell your Dialysis Doctor about this. Most commonly, the rhythm is sinus tachycardia, a rapid pulse of the normal heart beat, which is caused by dehydration (the removal of a large amount of fluid in a short amount of time). The heart tries to compensate for the sudden dehydration by speeding up. Depending on your other health problems, it can either be harmless, and gradually normalizing as you drink water, or it could cause other problems--for instance if you also have blocked arteries of the heart, just like running too far or too long with a rapid pulse for too long, it could trigger angina or (worst case) a heart attack. Other times, a pulse of 120 after dialysis could be caused by an arrhythmia, such as SVT (supra ventricular tachycardia). That might require an adjustment in your medications to try to keep the rhythm normal. Check with the Dialysis Doctor to find out whether there could be less fluid taken off during the session, or done more slowly, or if the doctor thinks you ought to see a Cardiologist about the heart rate. Good luck.