I understand your concern and I will do everything I can to answer your question. The brief answer: there is usually nothing to worry about. nerves that control the heart, the lungs, the diaphragm are all still developing and preparing the baby for birth. Often, the nerves activate prematurely or slightly irregularly. Most babies get hiccups before they are born because the nerves that control the diaphragm occasionally spasm, for example. The same happens in the nerves controlling the heart rate. If the structure of the heart, the amniotic fluid and baby s growth is ok, almost certainly, the baby will outgrow the irregular heart rate and everything will be ok when he or she is born. The testing your doctor has planned will detect any serious problem, but this is extremely rare in babies with PVC s (premature ventricular contractions). Here is a link that should also provide some reassurance http://pediatricheartspecialists.com/articles/detail/premature_ventricular_contractions_pvcs I hope that helps and best of luck to you