What type of receptors do beta blockers affect?

They block adrenergic receptors, or the receptors that react to epinephrine to accelerate and strengthen the heart rate.
Since they block epinephrine, beta blockers slow the heart rate down.
WPW is an abnormal conduction of impulses through abnormal nerve bundles (the bundles of Kent) in the heart wall. While it is often asymptomatic, it can cause tachycardia, or abnormally fast (and inefficient) heart beats. Since the stroke volume is diminished because the ventricles do not have time to fill completely before they contract, dizziness is a common symptom because the brain cells, as all other cells, are not receiving the proper amount of oxygen because they are not receiving the proper amount of blood per beat. Since beta blockers slow this abnormal transmission down, the heart stabilizes to a normal beating pattern, thereby restoring normal blood flow to the brain and, in fact, to the entire body and the dizziness abates.