Variability of paradoxical jet flow in a case of hypertrophic cardiomyopathy with midventricular obstruction was examined. Propranolol decreased both peak diastolic paradoxical jet flow velocity and peak systolic velocity at the narrowing portion. Nitroglycerin decreased peak diastolic paradoxical jet flow velocity with an increase in peak systolic velocity at the narrowing portion. Thus the diastolic paradoxical jet flow is dynamic as well as the abnormal systolic flow; however, changes in these abnormal flow dynamics may not be necessarily in the same direction. Doppler echocardiography should be useful in assessing effects of interventions on the flow dynamics in patients with hypertrophic cardiomyopathy with midventricular obstruction.