Interference with the normal transmission of electrical impulses through the conducting system of the heart. The condition is seen on electrocardiogram as a prolongation of the P-R interval, a widening of the QRS complex, a delay in the appearance of an expected beat, the loss of synchrony of atrial and ventricular beats, or dropped (missing) beats.

ETIOLOGY
Heart block may be produced by temporary changes in vagal tone, drugs or toxins (such as some antiarrhythmics or antihypertensives), infections (such as infective endocarditis or Lyme disease), fibrosis or other degenerative diseases of the conducting system, ischemia or infarction, or other mechanisms.