What would cause an irregular heartbeat?

My husband occasionally would get an irregular heartbeat but lately it is becoming more frequent. I've listened to his chest & it sounds like it beats normally for about 5 or 6 beats & then beats really fast for 3 beats or so. He's been tested for the stress test & had to wear a heart monitor for a day (a few months ago) but the tests didn't reveal any irregularities. He wants to go see a specialist. Anyone know what this could be?

Is he on stimulants e.g. smoking, etc. well the cause is there, as far as how many irregular beats are there, it can be easily in EKG long lead. Please take your husband to a good cardiologist, and have him assessed, because as you have mentioned it is increasing in frequency. I don't want you get confused with Holter's readings, OK.
Be practical.

my mother often get heart palpitations and she will jump for a second and then it goes away. they arent as frequent as your husbands heart speed-ups though. hope it helps!
get well soon!

It sounds like a run of 3 PVC's in a row, although not fatal, it should be checked out. It's odd that it didn't appear on the Holter or Stress Test, as these tests usually provoke the rhythm to appear. In this case, you should see either a Cardiologist, or an Electrophysiologist, both of these people can help you, although an Electrophysiologist is more skilled in the "electrical" parts of the heart, which is what an arrhythmia would be classified under. Your husband might need to wear an Cardiac Event monitor - a device that is worn continuously for a period of 30 days or longer to capture those "fast beats".