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A homogeneous T1 isointense and mildly T2 hyperintense to muscle infiltrative mass is centred at the inferior aspect of the left atrium, crossing the inter-atrial septum into the right atrium as well as infiltrating beyond the mitral annulus to the basal inferior left ventricular wall. A lobulated small frond-like component in the right atrium is minimally mobile, and not prolapsing into the right ventricle. No T1 hyperintensity to suggest the presence of fat within the mass.

Perfusion imaging shows relatively hypovascularity, and mild enhancement is demonstrated on both early and late gadolinium imaging. Normal LV function with ejection fraction 62%. No solid component is seen within a moderate to large pericardial effusion. 

Conclusion: Mildly enhancing hypovascular soft tissue mass that is homogeneously T1 isointense and mildly T2 hyperintense to muscle centred at the left atrium infiltrates through the interatrial septum into the RA and through the mitral annulus into the basal inferior LV wall. Moderate pericardial effusion without MRI evidence of tamponade.