The incremental shuttle walking test (ISWT) is recommended to assess the exercise capacity of patients attending cardiac rehabilitation (CR) as a cost-effective alternative to the treadmill test. We used the Bland Altman limits of agreement method on 353 paired ISWTs to explore whether the recommended practice test is necessary. The mean increase in distance from the practice to the second walk was 29.5 m (95% CI 23.0, 36.0) p<0.001, confirming the need for the practice walk when undertaking the ISWT.