Clinical investigation of 31 patients with idiopathic hypertrophic subaortal stenosis (IHSS) and idiopathic hypertrophic nonobstructive cardiomyopathy (IHNCMP) comprised electro- and phonocardiography, roentgenologic examination and echocardiography. The disease was latent in 3 patients, and ischemic heart disease or rheumatic heart lesion had been diagnosed prior to echocardiography in 26. Asymmetrical hypertrophy and hypokinesia of the upper third of the ventricular septum, narrowed left-ventricular cavity and septum-wise systolic movement of the anterior mitral cusp were findings common to all IHSS patients. The ventricular septum/left-ventricular posterior wall thickness ratio was elevated (1.42 +/- 0.06). In IHNCMP patients, this ratio was within normal range. The results of an acute pharmacologic test with 10 mg intravenous obsidan given to 10 IHSS patients suggested that the obstruction of left-ventricular outflow pathway was somewhat reduced. Prolonged (2 months to 3 years) obsidan treatment was given to 25 patients and was associated with positive effect in terms of improved subjective manifestations of the disease. However, echocardiographic patterns only showed moderate improvement in 9 of the 13 patients who had completed 1-3 years' treatment course.