An automated lidocaine infusion system has been developed for the treatment of ventricular arrhythmias. A drug serum concentration which is in the therapeutic range is initially achieved and maintained by an open-loop infusion regimen. The lidocaine infusion rate is then adjusted using closed-loop control to regulate the rate of premature ventricular contractions (PVC rate) at a setpoint. The major system components are a portable computer, a computer-controlled drug infusion pump, and an arrhythmia monitor which is used to measure the PVC rate. During closed-loop control, the drug infusion rate is constrained to keep the predicted serum concentration below an upper limit (ceiling concentration) so that toxic serum concentrations are avoided. The infusion rate is also constrained to keep the predicted serum concentration above a minimum value (floor concentration) to ensure the maintenance of a therapeutic serum level during closed-loop control. The system has been evaluated in initial clinical trials.