I've been experiencing heart palpitations and saw my doctor about them. They are likely benign PVCs - premature ventricular contractions. They might possibly be caused by my taking Singulair for shortness of breath due to allergies. I had a heart ultrasound which was entirely normal and now my doctor will be having me wear a Holter monitor to record my hearts electrical activity over a 24 hour period, to help them understand better what might be causing these palpitations. I've been experiencing PVCs off and on for probably the better part of 20 years although they seem to have been far more frequent the last few months, which also coincides somewhat with being on Singulair. My doc has me stopped on Singulair for the next two weeks to see if there's any change. I was told that while I wear the monitor I should go about my daily routine which will include my 23 mile round trip bike commute. My doc especially wants to see what happens when I exercise since benign PVCs typically subside under physical activity. The person at the clinic where they fit you for the monitor said that excessive sweating can cause leads to come off where they stick them on your skin. I'm thinking I can dial back the intensity of my commute somewhat seeing as how typically I do work up a pretty good sweat even with it being cold out. Any thoughts? Has anyone else gone through this or something similar?