The flow dynamics of midventricular obstruction in hypertrophic cardiomyopathy were evaluated with intravenous injection of sonicated albumin in 14 patients with vague velocity profiles on conventional continuous wave Doppler echocardiography. Nine patients (64%) demonstrated a clear envelope after the injection. The following three patterns of continuous Doppler profiles were obtained : 1) a monophasic flow profile with a brief and sharp increase in peak velocity in late systole, 2) a late-peaking systolic flow and a diastolic flow during isovolumic relaxation time emerging after sonicated albumin injection (biphasic flow profile), 3) a biphasic flow profile with systolic and diastolic flow waves having a notch around the second heart sound. The calculated peak pressure gradients from the modified Bernoulli equation did not differ significantly with the presence of diastolic wave or the site of obstruction. Therefore, these are independent parameters for estimating the severity of midventricular obstruction. Therefore, these are independent parameters for estimating the severity of midventricular obstruction. The sonicated albumin method was useful in delineating the flow profile, and thus evaluating the hemodynamics of midventricular obstruction in hypertrophic cardiomyopathy.