Twelve men suffering from the primary hyperkinetic heart syndrome (PHHS) displayed palpitation, rapid and forceful heart action, increased pulsations of the large arteries, cardiac systolic murmur, and the following circulatory values (averages): systolic arterial pressure (SAP) =154 mm Hg; heart rate (HR)=91 b/min; cardiac index (Ci) =5494 ml/min/m2; left ventricular mean systolic ejection rate index (SMEJR) =227 ml/min/m2; left ventricular mean pre-ejection delta P/delta t (delta P/delta t) = 1.32 mm Hg/msec. A two-year followup during which propranolol was administered (80-160 mg/day) revealed good subjective improvement and disappearance of signs of circulatory hyperkinesis. At the end of this period the hemodynamic functions were as follows: SAP=134; HR=69; Cl=3489; MSEJR=171; delta P/delta t=0.89. Substitution of placebo for the active drug caused prompt reappearance of symptoms of cardiac overactivity in each patient, and brought the circulatory functions back to these levels: SAP=157; HR=96; Cl=5530; MSEJR=245; delta P/delta t=1.33. These findings lend further credence to the concept that the PHHS is, indeed, a definable disease entity; they also document that propranolol ameliorates the symptoms of the disease but is ineffective for the underlying disorder.