25 patients affected by Primary Hypothyroidism and a control group of 25 subjects were studied with M-mode and Two-dimensional echocardiography. In hypothyroid patients mean left ventricular and aortic root dimensions were normal compared to control subjects. Pericardial effusion was found in 22 out of 25 patients (88%). Septal hypertrophy was found in 12 hypothyroid patients (48%), only in 3 out of these 12 patients left ventricular posterior wall hypertrophy was found. A moderate left atrial enlargement was found in 7 out of 25 hypothyroid patients. Two-dimensional echocardiography revealed an uniform degree of parietal hypertrophy from the basal segments to the cardiac apex. Therefore the main echocardiographic findings in hypothyroidism are: presence of pericardial effusion and asymmetrical septal hypertrophy. No correlations between these echocardiographic findings and age of patients, severity of "biochemical" alterations and duration of the thyroid disease was observed.