Background. Fabry disease is an X-linked genetic disorder resulting in the accumulation of glycosphingolipids in various organs, leading to exercise intolerance and early mortality. Enzyme replacement therapy (ERT) has recently been approved for use in Fabry patients. Goals of study. To assess baseline cardiopulmonary exercise characteristics in both invasive and noninvasive tests and to study the impact of ERT on exercise. Methods. A total of 15 patients with Fabry disease underwent baseline cardiopulmonary exercise tests. Six patients were randomized 2:1 to receive either ERT or placebo. We performed serial cardiopulmonary exercise tests at baseline and every 3 months over a period of at least 18 months. The baseline test was compared to the last two exercise tests for each patient. Results. Mean age was 32 years. Mean VO₂ max was 1.680 ± 0.67 L/min and increased by 0.459 ± 0.64 L/min in the patients receiving ERT. Mean VO₂ max was 1.462 ± 0.25 L/min and decreased by 0.116 ± 0.44 L/min in patients on placebo. Mean oxygen pulse (VO₂/HR) increased by 1.71 with enzyme, but increased only 0.025 in patients taking placebo. Estimated stroke volume (SV) increased by 10 ml in patients on ERT. Conclusions. In this small cohort, exercise tolerance increased in patients receiving enzyme replacement therapy. Cardiopulmonary exercise testing is a useful test in measuring the response to therapy in Fabry disease patients.