A fatal case of sinus standstill followed intravenous injection of therapeutic doses of lidocaine hydrochloride. The patient had congestive heart failure, but had no "sick sinus syndrome." To our knowledge, serious, adverse effects of lidocaine on sinus node function have not been reported previously. Our experience suggests that clinical assessment of the cardiac status is an important consideration in selecting a therapeutic dose of lidocaine. All patients receiving this drug require observation for adverse effects, even if doses are within the currently recommended ranges.