Anthracycline induced late onset cardiotoxicity, defined in terms of abnormal findings on echocardiography, has been reported to occur in 57% of childhood cancer survivors. Serial monitoring of cardiac function by means of echocardiography detects cardiac toxicity only when many of the cardiomyocites have already been damaged. Given the lack of evidence to support the reliability of serum markers of cardiotoxicity, many recommend modifying the dose of anthracyclines only when there is objective evidence of myocardial dysfunction by echocardigraphy. This approach could be responsible for the increasing frequency of dilated cardiomyopathy occurring 10-15 years after treatment. Non invasive imaging methods are thus critically needed to more precisely detect cardiotoxic changes in children receiving anthracyclines. CMRI has become the gold standard for the assessment and quantification of ventricular volumes, myocardial mass and global and regional wall function. CMRI also allows morphologic analysis of the myocardium as well as detection and characterization of pathological myocardium. In this study, the investigator therefore proposes to use serial MRI parameters in conjunction with a battery of serologic markers, obtained at intervals determined by cumulative anthracycline dose, to monitor changes in systolic function during chemotherapy and one year after the end of chemotherapy. The investigator will use a combination of a serum cardiac biomarker of inflammation (CRP), myocyte injury (Troponin, Caspases), heart failure (BNP), and extracellular matrix remodeling (PICP, CITP, Bone Alkaline Phosphatase, MMPs, TIMPs). The investigator will then correlate these findings with CMRI parameters of myocyte dysfunction. Results will be compared with standard echocardiography. The investigator predict that CMRI is a better indicator of early anthracycline cardiotoxicity in children with solid tumors and hematologic malignancies.