During that time, he was responsible for developing many of UNICEF's policies for children and served under three executive directors.
He started his career in UNICEF as the Deputy Executive Director in charge of Operations in 1949 and soon developed a reputation for his intellect, efficiency and dedication.
He played a leading role in integrating UNICEF into the United Nations Development Programme established in the late 1950s.
Heyward became a Deputy Executive Director of UNICEF in 1975 with the rank of UN Assistant Secretary General.
UNICEF committed to this model in 1976 and the organisation was working with the WHO in adopting a preventative approach to health care.