Heart-rhythm conditions, explained.

An irregular, often rapid heartbeat that starts in the upper chambers of the heart. AFib is the most common sustained arrhythmia and a leading cause of stroke.

A breakdown in the electrical wiring between the upper and lower chambers of the heart. The severity ranges from a harmless delay to a complete disconnection that requires a pacemaker.

The awareness of your own heartbeat — usually as a flutter, skip, thud, or racing sensation. Common, usually harmless, but occasionally the first clue to an arrhythmia worth treating.

A condition where the heart's natural pacemaker becomes unreliable — pacing too slowly, pausing, or failing to speed up appropriately with activity. Pacemakers are the definitive treatment when symptoms are present.

A family of fast heart rhythms that start above the ventricles and turn on and off abruptly. Most forms are not dangerous, and catheter ablation cures the vast majority of them.

A fast heart rhythm that originates from the lower chambers of the heart. Depending on its cause, VT ranges from a benign nuisance to the most common mechanism of sudden cardiac death.

A sudden, brief loss of consciousness caused by a temporary drop in blood flow to the brain. Most syncope is benign, but a small subset has a cardiac cause that we need to identify.

An inherited electrical condition with a characteristic ECG pattern and a small but real risk of sudden cardiac death, often during sleep or fever. Recognizing it early lets us avoid triggers and protect the highest-risk patients with an ICD.

A genetic condition in which the heart muscle becomes abnormally thickened. Most patients live full lives; a minority face sudden-death risk or symptoms from obstruction that need targeted treatment.

An electrical condition — either inherited or triggered by medications — that prolongs the heart's recovery time after each beat and predisposes to a specific dangerous rhythm called torsades de pointes.

When the heart's pumping strength is reduced, two things go wrong: forward flow weakens, and the risk of dangerous rhythms rises. Cardiac resynchronization and defibrillators address different parts of that problem.