3. Figures about the volume of procedures undertaken in the early period are patchy. In 1973 around 25,000 operations were performed in the US and this increased to 70,000 by 1977 (OTA, 1978). Elsewhere, the absolute numbers of procedures was small in comparison. In the UK for example 2,297 operations were carried out in 1977 and this increased to 4,057 by 1980 (British Heart Foundation, 2004)