Dual chamber pacing may be used as an alternative in the treatment of selected patients who are refractory to conventional medical treatment of hypertrophic obstructive cardiomyopathy. When programming the pacemaker it is essential to know the value of the atrio-ventricular interval which is able to cause the greatest reduction in the left ventricle outflow tract pressure gradient. We have used isoproterenol to calculate the parameter mentioned above. This allowed us to know the optimum value, not only in non-active conditions, but also reproducing the changes in the pressure gradient in different physiological situations.