 Martin Sheen (qv) had a heart attack during the filming and some  shots of Willards back are of doubles, including Sheens brother  who was flown out specially. Coppola was so worried that backing  would be withdrawn by the studio and distributor if news of Sheens  heart attack leaked out, that he kept it quiet, even to the extent  of explaining Sheens hospitalization as being due to "heat  exhaustion" in the official Shoot Schedule.