Among 30 patients with ventricular arrhythmia resistant to conventional antiarrhythmic therapy, 33% showed normalization of heart rhythm after single i.v. injection of Craviten at a dose of 6 mg. In all patients, sensitive and resistant to this dose of Craviten, serum dopamine beta-hydroxylase activity was initially twice as high as that in healthy controls. After Craviten administration, enzyme activity normalized in the sensitive persons only, parallelly with rhythm normalization. In this group of patients the initially increased erythrocyte membrane ATPase activities (total and ouabain-insensitive) also normalized.