BACKGROUND: Exercise capacity assessed by cardiopulmonary exercise testing is usually measured by peak oxygen consumption (V˙ O2). However, not uncommonly, patients achieve a relatively higher work load (peak work) compared to their peakV˙O2. In these situations it is difficult to know which parameter to use in assessing exercise capacity. The purpose of this study was to determine whether there are distinguishing physiological characteristics of patients with discordance between percent-of-predicted peak work versus peak V˙O2, in order to understand how to use these measurements in interpreting exercise capacity