The upper strip shown here is from a 23 year old female long distance runner with no known heart disease. There is sinus bradycardia with an RR interval of 1.30 seconds (this translates to a rate 45 bpm) and a normal PR interval of 0.16 seconds This heart rate is very common, indeed characteristic, in well trained athletes.
The lower strip is from a 65 male receiving a beta adrenergic blocking agent as part of treatment for hypertension. The heart rate is even slower with an RR interval of 1.6 seconds (rate = 38 bpm). The PR interval is normal (0.18 seconds).