Background. Cardiopulmonary exercise testing (CPET) is a non-invasive, objective and provides relevant information for clinical decision making. The purpose of the present study was to evaluate the cause for unexplained breathlessness by performing cardiopulmonary exercise testing. Methods. We carried out a retrospective analysis of CPET performed for 51 patients with unexplained breathlessness over a one-year period. Cardiopulmonary exercise testing was done by maximum symptom limited incremental protocol on a treadmill. Results. The mean age was 45 years (range 20-74 years). Mean body mass index (BMI) was 26.4; 7 (14%) subjects had a normal BMI, 12 (23%) were overweight, 30 (59%) were obese and 2 (4%) were underweight. Thirty-one (61%) patients achieved anaerobic threshold (AT). Based on the AT percentage criteria, 4% were classified as diseased, 17% as deconditioned, 20% as sedentary and 20% as normal. Fourteen (27%) patients had VO2 max >80% predicted. In the final analysis, 11 (22%) patients had ventilatory limitation, 16 (31%) had cardiovascular, 9 (17%) had mixed pulmonary and cardiac, 3 (6.5%) had musculoskeletal limitation and 3 (6.5%) had obesity as exclusive cause for breathlessness. Nine (17%) had normal studies with abnormal perception of breathlessness and they were advised to gradually increase their exercise levels. Conclusions. Cardiopulmonary exercise testing is a useful tool in the evaluation of dyspnoea disproportionate to clinical findings and standard tests. Although CPET points out the organ causing dyspnoea, organ specific investigation is required to plan the management.