To study the myocardial perfusion in primary hypothyroidism accompanied by cardiac pain feelings, a total of 21 patients aged 30-60 years were examined by using resting 201Tl myocardial scintigraphy and in combination with bicycle ergometric testing. At rest all the patients showed impaired myocardial perfusion. A decrease in 201Tl accumulation, which corresponded to the areas of impaired perfusion, was observed in 54% of segments. A severe impairment of myocardial 201Tl washout was recorded in all the patients. During exercise 201Tl myocardial scintigraphy, steady-state myocardial perfusion impairments with normal washout were recorded in most patients. Areas of transient myocardial ischemia were revealed in 3 patients during scintigraphy in combination with bicycle ergometric testing. The findings suggest that patients with primary hypothyroidism have myocardial perfusion impairments which are likely to be reflected by dystrophic processes. Along with these abnormalities, exercise myocardial scintigraphy makes it possible to detect transient perfusion alterations in some patients, which indicates that they have myocardial ischemia.