Twenty-six patients were treated for ventricular septal rupture following myocardial infarction over a five year period. Twenty-three patients underwent full haemodynamic investigation with a view to surgery and nineteen underwent operative closure of the defect. Overall hospital mortality was 47 per cent in the surgical group. Eleven patients had surgery within two weeks of infarction because of marked haemodynamic deterioration soon after septal rupture but only two survived to leave hospital. Eight patients underwent operation two weeks or longer after infaction, all were alive and well at discharge from hospital, six were well at one year and four at three years. Seven patients did not undergo surgery and the maximum survival for these was eight months. No patient in cardiogenic shock before septal rupture benefited from repair. Rapid clinical deterioration following rupture carried a poor prognosis. In all the shunt was large and medical treatment was ineffective. It is concluded that early surgical repair should be considered except when cardiogenic shock antedates the septal rupture.