Hypokalemia as a typical feature of primary aldosteronism (PA) is associated with muscle weakness and could contribute to lower cardio pulmonary fitness. The aim of this study was to describe cardiopulmonary fitness and exercise blood pressure and their determinants during a symptom-limited exercise stress test in patients with PA. We performed a cross-sectional study of patients with confirmed PA who were included before adrenal vein sampling on whom a symptom-limited exercise stress test with expired gas analysis was performed. Patients were switched to the treatment with doxazosin and verapamil at least tw o weeks befor e the study. In 27 patients (17 male) the VO 2peak was 25.4± 6.0 ml/k g/min which corresponds to 80.8 ±18.9 % of Czech national norm. Linear regression analysis shows that VO 2peak de pends on doxazosin dose (DX) (p=0.001) and kal emia (p= 0.02): VO 2peak = 4.2 - 1.0 * DX + 7.6 * Ka lemia. Patients with higher doxazosin doses had a longer history of hypertension and had used more antihypertensives before examination, thus indicating that VO 2peak also depends on the severity of hypertension. In patients with PA, lower cardiopulmonary fitness depends inversely on the severity of hypertension and o n lower plasma potassium level., V. Tuka, M. Matoulek, T. Zelinka, J. Rosa, O. Petrák, O. Mikeš, Z. Krátká, B. Štrauch, R. Holaj, J. Widimský Jr., and Obsahuje bibliografii