ObjectiveTo study the effect of serum from patients with fungemia and control patients on sinoatrial node function.DesignProspective, observational study.SettingSurgical ICU in a university hospital.PatientsFourteen patients with fungemia and 14 control patients.Measurements and Main ResultsSerum samples from all patients were assayed in anin vitrosinus node preparation. Serum samples from 11 (78%) of the 14 fungemic patients caused a decrease in sinus node activity, while serum samples from only one (7%) of 14 control patients caused slowing of the sinus node.ConclusionsSerum from many patients with fungemia causes slowing of anin vitrosinus node preparation. Thisin vitrofinding may explain bradyarrhythmias seen clinically in the setting of fungemia.