In patients, without clinical signs of myocardial impairment, who needed a transvenous cardiac pacing system, the phenomen of frequency potentiation was studied. For this purpose, “test contractions” were used, elicited 300 to 1000 msec after artificial rhythmical stimulation with basic frequencies in the range of 80 to 170/min. The left ventricular pressure (Brockenbrough catheter via the transseptal route), the aortic pressure (Odman Ledin catheter) and the ECG (lead II) were recorded. At comparable hemodynamic conditions (equal aortic and left ventricular end diastolic pressure) the left ventricular pressure pulse was found to increase not more than 20% after a rise in stimulation rate from 100 to 175/min. From this finding it is concluded, that frequency potentiation is minimal in the human myocardium.