<prompt> An adult presents to a physician because of repeated episodes of fainting. EKG fails to disclose an arrhythmia. Echocardiogram shows a mass in the left atrium that is acting like a ball valve to produce intermittent obstruction of flow. Which of the following would most likely be seen on microscopic examination of the resected mass?Benign myxoid tumorBenign tumor with gland formationBenign tumor with striated muscle differentiationMalignant tumor with gland formation  <response>: The most common primary cardiac tumor of adults is the benign atrial myxoma. 90 of these lesions involve the left atrium, where they can produce intermittent obstruction when they flop onto the mitral valve. Resection is curative. Neither benign adenomas nor malignant adenocarcinomas primary glandular tumors usually involve the hea. If adenocarcinoma is seen, suspect metastatic disease. The rhabdomyoma is the benign tumor with striated muscle differentiation choice C that can involve the hea. This tumor is the most common cardiac tumor of children. Ref: Wyatt C., Butterwoh IV J.F., Moos P.J., Mackey D.C., Brown T.G. 2008. Chapter 10. Cardiac Pathology. In C. Wyatt, J.F. Butterwoh IV, P.J. Moos, D.C. Mackey, T.G. Brown Eds, Pathology: The Big Picture. 