Edema is a generic component of the tissue response to acute injury and, therefore, an important diagnostic target for assessing the acuity of tissue damage in vivo. In the past, edema could not be used as a diagnostic target, because even histological techniques failed to provide reliable qualitative or even quantitative data on its presence, extent, and regional distribution. Cardiac MRI is about to change that. Using water-sensitive MRI, visualization of myocardial edema in vivo is possible within a few breath holds, without using radiation or contrast agents. Edema imaging provides useful incremental diagnostic and prognostic information in a variety of clinical settings associated with suspected acute myocardial injury. In combination with scar imaging, MRI differentiates reversible from irreversible injury and can quantify myocardial salvage after coronary revascularization. With this unique contribution, MRI of edema should be considered an essential diagnostic tool and, as part of a multitarget MRI scan, illustrates the exceptional role of comprehensive cardiac MRI in diagnosing and staging myocardial diseases safely and efficiently.