When Renzo Rivolta died in 1966 aged 55, his 26 year old son Piero took over the business. The first thing he did was design a four-door car which was shown in Frankfurt in 1967 as the ISO S4-Fidia. The body had been designed by the then still young Giorgetto Giugiaro and the car was built by his boss's company of Ghia in Turin. This was a large car with a 2,850 mm (112 in) wheelbase. The length from bumper to bumper was 4,970 mm (195 in). At first known as the S4 - the S4-Fidia name did not come into use until 1969 - this was available in two models with a choice of two engines, although initially only with a Chevrolet Corvette 327 engine of 5,354 cc; the Ford V-8 engine came later. Piero Rivolta claimed that his Fidia was the fastest production saloon in the world. The top speed was between 137 and 144 mph (220 - 230 kph) so he certainly did not have many cars that could keep up with it. Such performance was certainly remarkable for a car that weighed 1,620 kg (3,564 lb).
The ISO Fidia was an expensive car. It cost more than a 4-door Maserati and was more than twice the price of a Jaguar XJ6 with a 4.2 litre engine.