What are the most common effects of sinus bradycardia?

Usually nothing: Sinus bradycardia is usually a normal rhythm that occurs during sleep or in a highly conditioned athlete. As long as the rhythm is originating from the sinus node, the individual is usually asymptomatic. Slow heart rates associated with abnormal rhythms (such as third degree heart block) may not be tolerated and may be dangerous. Sinus bradycardia can also be a sign of other non-cardiac problems.