Arrhythmias:
Narrow-complex tachycardias
Wide-complex tachycardias
AV blocks
Second Degree AV Block Type I (Wenckeback)
Second Degree AV Block Type II
Third Degree AV Block
Premature atrial contraction
Premature junctional contraction<unk> 
Sick sinus syndrome
Non-arrhythmic cardiac causes:
Acute coronary syndrome
Cardiomyopathy
Congenital heart disease
Congestive heart failure (CHF)
Mitral valve prolapse
Pacemaker complication
Pericarditis
Myocarditis
Valvular disease
Psychiatric causes:
Panic attack
Anxiety
Somatic Symptom Disorder
Drugs and Medications:
Alcohol
Caffeine
Drugs of abuse (e.g. cocaine)
Medications (e.g. digoxin, theophylline)
Tobacco
Misc
Anemia
Hyperthyroidism
Pulmonary embolism
Dehydration
Sepsis
Pheochromocytoma
Narrow-complex tachycardias
Wide-complex tachycardias
AV blocks
Second Degree AV Block Type I (Wenckeback)
Second Degree AV Block Type II
Third Degree AV Block
Premature atrial contraction
Premature junctional contraction<unk> 
Sick sinus syndrome
Second Degree AV Block Type I (Wenckeback)
Second Degree AV Block Type II
Third Degree AV Block
Acute coronary syndrome
Cardiomyopathy
Congenital heart disease
Congestive heart failure (CHF)
Mitral valve prolapse
Pacemaker complication
Pericarditis
Myocarditis
Valvular disease
Panic attack
Anxiety
Somatic Symptom Disorder
Alcohol
Caffeine
Drugs of abuse (e.g. cocaine)
Medications (e.g. digoxin, theophylline)
Tobacco
Anemia
Hyperthyroidism
Pulmonary embolism
Dehydration
Sepsis
Pheochromocytoma
Premature ventricular contraction
Arrhythmias:
Premature atrial contraction
Narrow-complex tachycardias
Premature junctional contraction
Wide-complex tachycardias
Wandering atrial pacemaker
AV blocks