CMR has a key role in the evaluation of a number of cardiac pathologies and in various important clinical scenarios. CMR has become the gold standard for evaluating left ventricular and right ventricular volumes and function. The late gadolinium enhancement (LGE) technique is the most accurate clinical technique for the detection and quantification of myocardial infarction and scar. The use of velocity encoded (VENC) imaging enable accurate measurements of valvular heart disease and quantification of myocardial shunts. CMR’s unique ability to perform tissue characterization, including the ability to detect myocardial edema and inflammation, the ability to detect iron-overload, and the ability to quantify diffuse infiltration and scarring provide unique tools in a variety of clinical scenarios. We will review how these techniques are used in multiple clinical scenarios where CMR has proven diagnostic utility.CMR has become a well-established technique for the diagnosis of congenital heart disease, for determining surgical planning, and for evaluation of complications of congenital heart disease. In complex congenital heart disease CMR has the ability to provide both anatomical and functional/hemodynamic information which can provide the direction and magnitude of flow between structures. Often it is difficult to see other vascular structures within the chest by echocardiography which are easily seen by CMR. CMR can more easily visualize some more common congenital abnormalities such as sinus venosus atrial septal defects, and can more easily detect anomalous pulmonary veins. In the follow up of congenital heart conditions such as Tetrology of Fallot, CMR can evaluate for residual ventricular septal defects, evaluate right ventricular size and function, and can assess the severity of pulmonic regurgitation. In patients with arterial switch procedures for transposition of the great arteries, CMR can evaluate differential flows in the branch pulmonary arteries and detect PA stenosis. In patients which have undergone a Fontan procedure, CMR can evaluate the presence of shut leaks, stenosis and thrombosis. The velocity encoding technique is also useful for measuring the magnitude of cardiac shunts which would otherwise need to be evaluated invasively. Emerging techniques such as 4D flow have potential to improve evaluation of congenital heart disease where multiple flows can be obtained simultaneously and all of the heart structures can be visualized throughout the cardiac cycle. New free-breathing techniques and self-navigation could provide important future roles for this application. The key reasons that CMR makes a difference: (1) ability to assess vascular anatomy and hemodynamics (2) ability to quantify myocardial chamber sizes and function (3) ability to assess valvular function and assess myocardial shunts.One important role for CMR is the evaluation of the etiology of new onset heart failure and cardiomyopathy. In the setting of an ischemic cardiomyopathy, LGE is often present in endocardial and transmural distributions which follow coronary distributions. The total burden of scar versus potentially viable myocardium can be assessed. Adenosine stress CMR can be used to detect the presence of perfusion abnormalities suggesting a potential ischemic etiology. The pattern of LGE can also help differentiate ischemic cardiomyopathy from non-ischemic cardiomyopathies. A number of non-ischemic cardiomyopathies have characteristic patterns of scar. Hypertrophic cardiomyopathy (HCM) can have patchy scar typically in the regions of myocardial hypertrophy and often in the anterior and inferior insertion sites. HCM is also characterized by increased Native T1, and increased extracellular volume (ECV). The presence and extent of scar in LGE predicts adverse cardiovascular outcomes including cardiac death, heart failure, and sudden cardiac death. Sarcoid cardiomyopathy is characterized by patchy scar which is often sub-epicardial with multiple foci. The presence of scar in sarcoidosis has also been shown to be associated with adverse cardiovascular outcomes. There is growing evidence that T2 mapping may also be able to detect myocardial inflammation in Sarcoid. Amyloid cardiomyopathy is associated with diffuse LGE, as well as increased ECV and Native T1. The presence of scar in Amyloid cardiomyopathy is also prognostically significant. It is important to differentiate between these causes of non-ischemic cardiomyopathies as they have different prognoses. The use of T2* imaging and mapping has revolutionized the care of patients with iron-overload cardiomyopathy where its use has translated into a significant reduction in mortality in combination with chelation therapy. In this clinical scenario, CMR is the only technique which can detect iron overload. T1 and T2 mapping have also played a role in the detection of iron overload cardiomyopathy. In diseases such as Anderson-Fabrey disease, myocardial T1 is markedly reduced which is providing a new diagnostic tool for this disease. The key reasons that CMR makes a difference: (1) Ability to detect myocardial scar and differentiate ischemic from non-ischemic cardiomyopathy. (2) scar patterns suggest specific non-ischemic cardiomyopathies. (3) Parametric mapping techniques can detect diffuse disease.Increasingly CMR is providing an important diagnostic tool for trying to determine the cardiovascular cause of increased troponin but non-obstructive coronary arteries in patients presenting with acute chest pain. In this clinical scenario CMR’s unique ability to accurately detect myocardial edema and fibrosis frequently provides the key to the diagnosis. In patients with possible myocarditis CMR can detect the presence of myocardial inflammation and edema using T2 mapping or T1 mapping. Furthermore, the presence of scar in a subepicardial distribution in the correct clinical context is usually diagnostic for myocarditis. In other cases, patients may have the presence of myocardial edema but the absence of myocardial scarring which can be helpful in differentiating takutsubo cardiomyopathy from an anterior myocardial infarction in in the setting of characteristic wall motion abnormalities. Occasionally, despite the presence of non-obstructive CAD, there will be evidence of an acute myocardial infarction on CMR as evidenced by myocardial edema, LGE, and microvascular obstruction. In a number of cases the etiology may be that a branch of a coronary artery is occluded which can sometimes be missed at the time of angiography. The key reasons CMR makes a difference: (1) ability to detect myocardial edema and myocardial fibrosis.The exquisite tissue characterization properties has made CMR indispensable for understanding the etiology of cardiac masses. CMR can easily differentiate structures which are mistaken for masses on other cardiac imaging modalities. CMR is very good at differentiating cardiac masses from cardiac thrombi based on tissue characteristics. Thrombi do not take up contrast on first-pass myocardial perfusion imaging and they appear dark on LGE images as they do not take up contrast. A number of specific contrast properties such as the T1 and T2, and LGE can help differentiate between certain types of tumors and masses. CMR can also provide important information about the location and size of the mass and what extracardiac structures may be involved. The key reason CMR makes a difference: (1) The ability to differentiate between cardiac masses and thrombi (2) the ability to provide tissue characterization with T1 and T2 imaging/mapping.CMR has unique abilities to characterize pericardial disease. CMR can provide anatomic detail to measure thickening of the pericardium. Myocardial tagging can be used to evaluate for the presence of myocardial tethering to the pericardium. Real time CMR can be used to detect the presence of ventricular interdependence which is a characteristic filling pattern of the ventricle in the presence of myocardial constriction. Finally, LGE can detect the presence of active pericardial inflammation. Key reasons CMR makes a difference: (1) Ability to characterize the anatomy and physiology of pericardial disease.CMR’s unique abilities to visualize anatomy and function, to characterize the myocardium, masses and pericardium, and the ability to accurately detect the presence, pattern and extent of scar play a key role of defining the role of CMR in multiple cardiac pathologies and important clinical diagnostic dilemmas.