Changes in hemodynamic and ECG variables following disopyramide (1.7 mg = 3.9 mmol/kg b.wt.) were studied in 9 patients with ventricular arrhythmias. All patients displayed a marked reduction in the number of ventricular ectopic beats, all except one exhibiting complete abolition of the arrhythmia for at least 30 min. QT and QRS intervals showed statistically significant prolongations, and thereafter decreased exponentially with time. Above a certain concentration threshold that varied between the patients, systolic time intervals and aortic (dp/dt)max showed linear changes with increasing drug serum levels. Changes in diastolic pulmonary artery pressure showed no simple relationship with disopyramide concentration or time after injection. In 3 out of 4 patients studied, there was a good correlation between the lowest level of disopyramide that elicited both an antiarrhythmic effect and a demonstrable decrease in cardiac contractility.