Regional myocardial function was studied using sonomicrometry in six mongrel dogs, anaesthetized with halothane (1% inspired), as increasing doses of verapamil were given i.v. In addition to a gradual increase in end-diastolic length and a reduction in systolic shortening, an abnormal (paradoxical) contraction pattern appeared in the apical region. This occurred in the absence of coronary artery damage and at coronary perfusion pressures unlikely to result in ischaemia. Administration of verapamil in the presence of halothane results in regional dysfunction similar to that caused by the intracoronary administration of nifedipine.