Adrenergic blocking agent affecting responsivity of the cardiovascular system and used to treat specific cardiovascular conditions such as high blood pressure and arrhythmias. Because they appear to dampen cardiovascular phasic responsiveness, beta blockers are of concern to PDD examiners because of their potential as a pharmacological countermeasure. Testing of examinees who take beta blockers is routine practice, as some cardiovascular responsiveness usually persists even with the medication.