Cardiac
Inferior MI (involving RCA)
Sick sinus syndrome
Neurocardiogenic/reflex-mediated
Increased ICP
Vasovagal reflex
Hypersensitive carotid sinus syndrome
Intra-abdominal hemorrhage (i.e. ruptured ectopic)
Metabolic/endocrine/environmental
Hyperkalemia
Hypothermia (Osborn waves on ECG)
Hypothyroidism
Myxedema coma
Hypoglycemia (neonates)
Toxicologic
B-blocker
Ca-channel blocker
Digoxin toxicity
Opioids
Organophosphates
Ethanol
Clonidine
Infectious/Postinfectious
Chagas disease
Lyme disease
Syphilis
Other
Brash syndrome
Inferior MI (involving RCA)
Sick sinus syndrome
Increased ICP
Vasovagal reflex
Hypersensitive carotid sinus syndrome
Intra-abdominal hemorrhage (i.e. ruptured ectopic)
Hyperkalemia
Hypothermia (Osborn waves on ECG)
Hypothyroidism
Myxedema coma
Hypoglycemia (neonates)
Myxedema coma
B-blocker
Ca-channel blocker
Digoxin toxicity
Opioids
Organophosphates
Ethanol
Clonidine
Chagas disease
Lyme disease
Syphilis
Brash syndrome
ACLS: Bradycardia
Cardiac
PALS: Bradycardia
Inferior MI 
ACLS: Tachycardia
Sick sinus syndrome
PALS: Tachycardia
Neurocardiogenic/reflex-mediated