I know what you mean, mine was explained as diastolic dysfunction and possible systolic function in the mix along with my very frequent pvc's and tachycardia episodes mostly related to my autonomic nervous system failure and miscommunication with the brain/heart.
My hr would go from 40's to 125 in a blink - less than a minute, then be steady at 60 or 70 and then turn around and be 195. I had a pacemaker/icd implanted for the bradycardia dx on a TTT where my heart stops and my bp tanks, which helped with the low hr's (with no meds). Now I can go from a set 60 to 195 with no exertion or provacation even at rest.
It's important to understand the autonomic nervous system and it's role it plays in blood pressure and heart rate - google the ANS or go to www.ndrf.org and read about it. Our dysautonomia forum here has a lot of info on the ANS and links to dr's who know about this and treat these disorders
http://www.medhelp.org/health_pages/Neurological-Disorders/Autonomic-Dysfunction-FAQ/show/181?cid=196
Another thing is, many meds do cause bradycardia, so it's important what your heart was doing before any meds were started, did you have this then or is this a side effect of medicine?
Children can have ANS issues also, I've had it since I was 9 but it took until I was 42 for a doctor to recognize the symptoms and send me for a tilt table test and check my bp/hr responses.