Fatal heart block due to mesothelioma of the atrioventricular node.

A fit young man of 23 was symptom free until the time of his death despite a narrow complex complete heart block, with resting heart rates down to 35 beats/min, that was first diagnosed when he was 10. The clinical diagnosis remained congenital heart block. Necropsy showed extensive infiltration of the atrioventricular node and proximal bundle by mesothelioma tissue. Pacing had not been advised because of his excellent exercise tolerance.