In order to identify the characteristics of subclinical hypothyroidism (SH) during physical stress and its recovery, 15 SH patients and 16 healthy women were compared by a treadmill cardiopulmonary test. Means of variables were analyzed by the Mann-Whitney U test. Patients obtained lower values for peak expired fraction of O2 (14.90+/-1.05 x 16+/-1.14%; p = 0.014); systolic blood pressure variation (34.33+/-17.92 x 52.50+/-17.22; p = 0.009); exercise duration (8.83+/-2.91 x 14.5+/-5.63 min; p = 0.0005), maximal test load (11.6+/-4.22 x 18.94+/-5.45%; p = 0.0004), as well as tendencies in gas exchange ratio and peak heart rate. Between the first and the third recovery minutes, there was a reduction of only 0.71 mmHg in the diastolic blood pressure, whereas there was a 5.33-mmHg reduction to control group (p = 0.0009) (slower recovery of patients). It is presumable that SH may cause cardiopulmonary dysfunctions, with higher sensibility to the parameters previously cited.