Two diverticula of the heart that caused no perceptible bulge in the cardiac outline were found at necropsy amongst 197 hearts from patients who had had myocardial infarcts. They lay within the wall of the left ventricle communicating with the left ventricular lumen by a small orifice, had mural thrombus in their lumens, were lined by connective tissue and surrounded by a healing or healed infarct. The lesions resulted from an incomplete rupture of the heart caused by the arrest of a haemorrhagic dissection en route from endocardial to epicardial surfaces through the infarcted ventricular wall. Resorption and organization occurred and a diverticulum formed. The distinct morphology of the diverticulum permits its differentiation from both a left ventricular aneurysm and a pseudoaneurysm.