My Husband, Age 74, Has A Low Heart Rate --

My husband, age 74, has a low heart rate -- as low as in the mid 40's resting and possibly even lower. He also experiences occasional vertigo for which he takes a blue pill we've been told is Dramamine or equivalent. He is a runner -- not long distance or even avid, anymore, but he does run several miles a week. He has a lot of trouble staying awake in front of the TV, and I think he has minor sleep apnea.
He has been checked by cardiologist -- year or more ago -- with no definitive problems detected. Should we worry? She we see another doctor?