The symptoms are predictable from knowing the electrical events in CHB. With the onset of CHB, asystole develops and brief syncope results, followed by rapid and full recovery of higher mental faculties as the escape rhythm develops, restoring cardiac output. Though the heart is beating slowly, the cardiac output is rarely depressed enough to cause symptoms at rest. However, the exercise heart rate and cardiac output are greatly depressed, resulting in effort breathlessness, fatigue, possibly angina, and tiredness. Examination shows bradycardia, AV dissociation in the venous pressure and variable intensity of the first heart sound, an ejection flow murmur and sometimes signs of heart failure.

The outlook in the absence of treatment is poor. Increasingly long episodes of asystole followed by increasingly slow escape beats are likely, resulting in further syncope, until finally asystole occurs not followed by a ventricular escape rhythm and death. Occasionally the bradycardia leads to a high-grade ventricular arrhythmia, often a long QT dependent arrhythmia such as torsade-de-pointes. Clearly this is lethal unless terminated quickly.

Most acquired CHB requires a permanent pacemaker. Whether a temporary pacemaker (‘wire’) is needed prior to the permanent pacemaker depends on the stability of the escape rhythm, the safety of temporary wire insertion locally and the delay in permanent pacemaker implantation. Unstable rhythms are those where syncope (i.e. significant asystole) has occurred, where the heart rate is very low (i.e. ≤ 30 b/min) or the QRS complex is broad. Escape beats with a continually changing QRS morphology indicate a very high risk of early asystole. Complete heart block that does not require a temporary or permanent pacemaker needs to have a stable escape rhythm and a reversible cause, e.g. CHB complicating an inferior wall ST segment elevation myocardial infarction (STEMI). Congenital CHB (due to maternal systemic lupus erythematosus [SLE] damaging fetal cardiac conducting tissue in utero) is often managed without pacing, though there is accumulating data that permanent pacemakers may prolong life.