Subclinical hyperthyroidism (SH) may be responsible for many cardiovascular 
changes, including an impaired exercise performance. The aim of our study was to 
evaluate the response to the treadmill cardiopulmonary test in patients with SH. 
We studied 14 female patients from our endocrine clinic with exogenous SH, free 
from cardiovascular diseases, with mean age of 38.6 +/- 10.2 years, body mass 
index (BMI) of 24.4 +/- 4.0 kg/m(2), and disease duration of 4.9 +/- 4.9 years. 
The mean serum thyrotropin (TSH) was 0.03 +/- 0.03 mU/L, serum free thyroxine 
(FT(4)), 1.72 +/- 0.21 ng/dL, and serum triiodothyronine level, 137 +/- 32 
ng/dL. The control group comprised 15 euthyroid, healthy women, with mean age of 
35.4 +/- 7.4 years and BMI of 27.3 +/- 5.9 kg/m(2). Both groups had a sedentary 
lifestyle and underwent the cardiopulmonary test using a treadmill with the 
Balke protocol. Gas concentrations and the respiratory outflow were measured and 
the electrocardiogram (ECG) was registered in real time. We calculated the 
minute ventilation (V(E)), the oxygen consumption (peak VO(2)), the carbonic gas 
exhalation (peak VCO(2)) and the anaerobic threshold (AT). The heart rate (HR) 
at rest (90.9 +/- 15.7 versus 78.9 +/- 8.7 beats per minute; p = 0.03) was 
higher in the patients from our clinic. There was no difference between groups 
regarding age, BMI, fat percentage, blood pressure, peak HR, exercise duration, 
mean treadmill peak inclination, V(E), peak VO(2), peak VCO(2), and AT. There 
was no correlation between peak VO(2) and FT(4), TSH, or disease duration. Our 
results show that exercise capacity in young and middle-aged female patients is 
not significantly affected by exogenous SH.