This study sought to evaluate the hypothesis that global longitudinal strain (GLS) guidance of cardioprotective therapy would improve cardiac function of at-risk patients undergoing potentially cardiotoxic chemotherapy, compared with usual care.The conventional criteria for diagnosis of chemotherapy-related cardiac dysfunction (CTRCD) are dependent on the recognition of heart failure symptoms and/or changes in left ventricular ejection fraction. However, the measurement variability of left ventricular ejection fraction necessitates broad diagnostic ranges, with the consequence of low sensitivity for CTRCD. Observational data have shown GLS to be a robust and sensitive marker to predict CTRCD and thereby guide the initiation of cardioprotective therapy, but these data are insufficient to justify changing the diagnostic criteria for CTRCD.The SUCCOUR (Strain sUrveillance of Chemotherapy for improving Cardiovascular Outcomes) trial is an international multicenter prospective randomized controlled trial. Patients who are taking cardiotoxic chemotherapy (n = 320) with at least 1 risk factor will be randomly allocated into GLS- and ejection fraction-guided strategies. All participants will be followed over 3 years for the primary endpoint (change in 3-dimensional ejection fraction) and other secondary endpoints.Among the first 185 patients (age 54 ± 13 years; 93% women) from 23 international sites, 88% had breast cancer, 9% had lymphoma, and 3% had other cancers. Heart failure risk factors were prevalent: 34% had hypertension and 10% had diabetes mellitus. The most common chemotherapy regimen during this study was the combination of anthracycline and trastuzumab. The baseline 3-dimensional left ventricular ejection fraction was 61 ± 4%, and GLS was 20.3 ± 2.5%. Of 93 patients followed up in the first year of the study, 10 had to withdraw for noncardiac reasons. Of 40 patients randomized to the GLS-guided arm, 15 have been started on cardioprotective therapy, whereas 4 of 46 patients in the ejection fraction-guided arm have been started on therapy.The SUCCOUR trial will be the first randomized controlled trial of GLS and will provide evidence to inform guidelines regarding the place of GLS for surveillance for CTRCD. (Strain sUrveillance of Chemotherapy for improving Cardiovascular Outcomes [SUCCOUR]; ANZ Clinical Trials ACTRN12614000341628).