Background and Aims Standardized definitions for outcome measures in randomized clinical trials and observational studies are essential for robust and valid evaluation of medical products, interventions, care, and outcomes. The European Unified Registries for Heart Care Evaluation and Randomised Trials (EuroHeart) project of the European Society of Cardiology aimed to create international data standards for cardiovascular clinical study outcome measures. Methods The EuroHeart methods for data standard development were used. From a Global Cardiovascular Outcomes Consortium of 82 experts, five Working Groups were formed to identify and define key outcome measures for: cardiovascular disease (generic outcomes), acute coronary syndrome and percutaneous coronary intervention (ACS/PCI), atrial fibrillation (AF), heart failure (HF) and transcatheter aortic valve implantation (TAVI). A systematic review of the literature informed a modified Delphi method to reach consensus on a final set of variables. For each variable, the Working Group provided a definition and categorized the variable as mandatory (Level 1) or optional (Level 2) based on its clinical importance and feasibility. Results Across the five domains, 24 Level 1 (generic: 5, ACS/PCI: 8, AF: 2; HF: 5, TAVI: 4) and 48 Level 2 (generic: 18, ACS-PCI: 7, AF: 6, HF: 2, TAVI: 15) outcome measures were defined. Conclusions Internationally derived and endorsed definitions for outcome measures for a range of common cardiovascular diseases and interventions are presented. These may be used for data alignment to enable high-quality observational and randomized clinical research, audit, and quality improvement for patient benefit.