Cardiac function in mild and severe primary hypothyroidism.

One hundred patients with mild to severe primary hypothyroidism have been analyzed for abnormalities in left ventricular performance utilizing noninvasive techniques. These studies have revealed significant abnormalities in cardiac function which correlated inversely with serum T4 levels. The abnormalities in cardiac function were completely reversible with thyroid hormone therapy. Even in patients with mild subclinical hypothyroidism, significant changes in left ventricular performance were achieved by doses of thyroid hormone which normalized TSH secretion. Therapy with either L-T4 or L-T3 resulted in normal cardiac function though L-T3 produced normal cardiac function on lower doses than were necessary to normalize TSH secretion. These studies are intended to provide new information on the optimal treatment of hypothyroidism.