Progressive atrioventricular block during exercise in univentricular heart.

Two patients who had univentricular heart presented with complaints of recurrent nausea and vomiting during exertion. Exercise study revealed 1:1 atrioventricular conduction and no symptoms at rest; at peak exercise, both patients experienced progressive, high grade, second degree atrioventricular block and nausea. Both patients underwent permanent pacemaker implantation, with relief of symptoms. Exercise testing is important in evaluating patients who are at increased risk of spontaneous atrioventricular block, and exertion-induced nausea may be a clue to its presence.