**6. Natural history**

The natural history of untreated PI-VSD is also poorly understood. As advances in the acute and chronic management of coronary artery disease continues to evolve, so does complications of CAD. In general, 25% of patients with PI-VSDs die within the first 24 hours (Berger, 1992). Death is most likely a function of pre-existing comoribidites and potentially irreversible and catastrophic heart failure that comes from not only the acute pump failure from the precipitating infarct but also the massive acute left to right heart shunting that compromises systemic perfusion further. The sudden increase in pulmonary overcirculation also contributes to the development of significant right heart failure. For those patients who survive the acute event, 1, 2, and 4-week survival is 50%, 35%, and 20% respectively (Lemery, 1992). It is easy to appreciate that those patients who survive the first month may have inherently favorable factors that might further self-select for a good post-operative outcome. Prolonged untreated survival has been reported with up to 7% of patient surviving to 1 year – obviously the physiologic insult and over-circulation is minimal.
