Though most cases are asymptomatic, the two main symptoms of bundle branch block are presyncope and syncope. Presyncope is a general term that refers to a feeling of lightheadedness that can lead to fainting. Syncope is the medical term for fainting or passing out, usually due to insufficient blood flow to the brain. When left bundle branch block occurs alongside other heart conditions and causes more severe symptoms, it often most exacerbates shortness of breath and fatigue.

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