Patients with chest pain and a prehospital ST-segment elevation myocardial infarction (STEMI) are preferably treated with immediate percutaneous coronary intervention (PCI). However, patients with normalization of symptoms and ST-segment elevation upon hospital arrival (transient STEMI) received inconsistent therapy due to logistic reasons and the absence of evidence or explicit guidelines. In this trial, the optimal timing of coronary angiography and subsequent revascularisation is investigated in patients presenting with transient STEMI. In this prospective, multicentre, randomized controlled clinical trial, 142 consecutive patients with initially acute chest pain and STEMI, whose symptoms and ST-segment elevation resolve upon admission, are randomized to immediate intervention or a delayed intervention. Primary outcome is infarct size measured at 4 days determined by cardiovascular magnetic resonance. Secondary outcomes are left ventricular function and volumes, myocardial salvage and microvascular injury at baseline; the change in left ventricular function, volumes and infarct size at 4 months; and major adverse cardiac events at 4 and 12 months. The TRANSIENT Trial evaluates whether a delayed invasive strategy (according to NSTEMI-guidelines) is superior to an immediate invasive strategy (according to STEMI-guidelines) in patients with a transient STEMI.