A long-standing conundrum: an unusual case of 2:1 atrioventricular block with conflicting findings.

A 2:1 atrioventricular (AV) block can occur anywhere within the conduction system, and noninvasive measurements may not always predict the exact site of the block. Although localization of the block is critical for deciding any treatment, patients should also be carefully questioned about symptoms both at rest and during exertion. A case of 2:1 AV block that was symptomatic only during exertion, appeared infranodal by noninvasive diagnostic methods, but was found to be intranodal on electrophysiological study is reported.