My husband was at the ER two days ago and his heart rate was 30 - 50 and the ER doc said its because he's very active true or not what should he do?

Why was in ER. The heart rate of 50 is acceptable if there are no symptoms related to it but 30 is very unusual and even if asymptomstic needs evaluation with ekg to check the rhythm and rate of thirty invariably will show evidence of complete heart block and no er doctor will ignore that.You say the rate was 30 to 50 which also does not make sense.If it is 30 needs cardiology consult as it can be dangerous.
Athletes Heart rates. Yes. Athletes in the prime of physical and cardiovascular fitness have very low heart rates. This means their hearts are pumping very efficiently. I cannot comment further because I have no idea from your question why he was in the er.
Needs an EKG. A fit person often has a heart rate in the 50s or 60s, but not the 30s. He should have an ekg to see if he has a heart conduction block. If so, he should be evaluated by a cardiologist to determine whether or not he needs a pacemaker.