Cystic medionecrosis of the coronary arteries and fatal coronary vasospasm. The histopathological basis of coronary vasospasm is not well defined. We report a patient with directly observed coronary artery spasm in whom cystic medionecrosis of the coronary arteries and great vessels and myxomatous degeneration of the mitral valve were evident. We suggest that myxoid connective tissue lesions of the heart may be linked to coronary vasospasm. 