It was not the ex-presidents first bout with irregular heartbeat: In May 1991, then-President Bush was admitted to Bethesda Naval Hospital after a White House physician determined his heart was beating rapidly and irregularly. Bushs condition then, it turned out, was not caused by underlying heart disease. Instead, he was diagnosed with Graves disease (242.0, toxic diffuse goiter; Graves disease), a thyroid condition that often causes heart disease, and was treated for atrial fibrillation with a combination of drugs: procainamide and digoxin to control the irregular heartbeats and coumadin to protect against blood clotting.