Does it feel like your heart skips a beat or "thumps"? Or does your heart flutter sometimes?
Either way, it could be anxiety causing it which, oddly enough, can make it worse. Anxiety causes the PVC's/arrhythmia which causes the anxiety. It's a horrible endless loop.
I dealt with this for, literally, years. It's nothing to worry about, but you may want to talk to your doctor about anxiety and mention the PVC's/arrhythmia.
Another possibility is that your electrolytes are out of whack, which can usually be cured by taking a multivitamin on a daily basis and/or drinking Gatorade or something like that.
But if it continues, you'll definitely want to see your doctor. If you start feeling chest pains, then you'll want to head to the ER.
I think remar pegged a good question, anxiety has hoardes of (innocent) symptoms.
What kind of "jumping"? What did it feel like, pounding or fluttering or skips? Anxiety, if that's the cause, can be the cause of the palpitations. It can also be the cause of several digestive disturbances too. It is wise to get checked out by your GP and see what he or she says. ;-)
Have you been diagnosed with anxiety? I'm not sure of your age. If you're young and in good health it's probably not your heart. It could be stomach problems. The best thing to do is see your Dr to find out what's going on.