Abstract
Cardiac blood cysts are very rare in adults. Their etiology, pathogenesis, and optimal management remain unclear. We report a case of a large left atrial cystic mass with clinical and imaging characteristics of a blood cyst that vanished between chest CT angiogram and trans-esophageal echocardiogram examinations done 2 days apart, without embolic phenomena. This patient likely had a blood cyst that spontaneously ruptured. This case is unusual since we did not find a case published in the English literature of a spontaneously ruptured blood cyst.