Objectives: Warm-up angina describes a reduction in angina, ischaemia and arrhythmias on second exercise in patients with coronary artery disease, after ‘warming-up’. The exact mechanism underlying this cardio-protection remains undefined, and may be explained by a relative reduction in myocardial strain. Cardiac magnetic resonance (CMR) compatible ergometers permit physiological responses to exercise to be studied with CMR imaging. CMR feature tracking (CMR-FT) is a novel method for quantification of myocardial strain from standard steady-state free precession (SSFP) images. We sought to determine whether there is a relative reduction in myocardial strain on second exercise.Methods: Patients with coronary artery disease awaiting intervention gave consent for supine cycle ergometry on a 3T Phillips Achieva CMR scanner with an MR compatible ergometer (Lode, Netherlands), using a standardised incremental exercise protocol. A standard series of SSFP sequences, were acquired at rest and during two consecutive periods of exercise (Ex1, Ex2), separated by a 20 min rest period. Myocardial deformation parameters were performed using custom software (Feature Tracking, Tomtec, Germany) to analyse standard SSFP cine images from the mid-left ventricular (LV) short axis slice. Data are presented as mean ± SD.Results: Ten patients (63.5 ± 8 years) completed the protocol. The table below shows the measured parameters. Time to angina increased on Ex2 (Ex1 173 vs Ex2 236 seconds) despite similar myocardial oxygen consumption (rate pressure product Ex1 19,834 vs Ex2 20,288 mmHg/second). Ex1 and Ex2 significantly increased heart rate and LV ejection fraction and decreased end systolic volume from rest. Seven patients were suitable for CMR-FT analysis. Radial and circumferential time to peak strain were significantly reduced and circumferential strain rate significantly increased with both Ex1 and Ex2 (vs rest). There were no differences between Ex1 and Ex2.Conclusion: Myocardial strain quantified using CMR-FT during exercise-induced ischaemia is feasible in patients with coronary artery disease. Exercise results in a significant increase in myocardial strain. However, despite the demonstration of a warm-up effect on second exercise, there were no significant differences in any parameters between Ex1 and Ex2. Cardio-protection from warm-up angina may therefore be explained by an enhanced resistance to ischaemia or relative redistribution of perfusion during second exercise.(Equation is included in full-text article.)