Sinus bradycardia is a sinus rhythm with a reduced rate of electrical discharge from the sinoatrial node, resulting in a bradycardia, a heart rate that is lower than the normal range (60–100 beats per minute for adult humans).

[3] The slow heart rate may also lead to atrial, junctional, or ventricular ectopic rhythms.

[medical citation needed] Sinus bradycardia can also be an adaptive advantage; for example, diving seals may have a heart rate as low as 12 beats per minute, helping them to conserve oxygen during long dives.

[4] Sinus bradycardia is a common condition found in both healthy individuals and those who are considered well-conditioned athletes.

Any recent changes to patient's medication history, new symptoms such as chest pain, shortness of breath and palpitations, family history of sinus bradycardia, physical exam that reveals cyanosis, peripheral edema, altered mental status, dyspnea, rales and crackles are all relevant information to consider for differential diagnosis.