It was during this time that Barlow became interested in auscultation and phonocardiography which led him to investigate non-ejection clicks and late systolic murmurs.

Barlow noticed that the man had a single fibrosed mitral valve chord, he also noted no abnormality outside the heart to account for the click.

Barlow, by further investigation, was able to demonstrate that the cause of this widely known but little-understood problem was due to a pathological condition of the mitral valve.

[3] In 1972, together with Margaret McClaren and others, he carried out a study on 12,000 schoolchildren of Soweto which demonstrated very high levels of rheumatic heart disease.

When the paper was published in the British Medical Journal the international publicity highlighted the poor socio-economic conditions of the children living under the laws of apartheid, the South African government was critical of the study.

[3] Barlow was widely acknowledged by his peers as an excellent clinician who put great store into taking a careful medical history and a thorough physical examination.

In 1968 Barlow and Wendy Pocock co-authored a paper published by the British Heart Journal[4] Perspectives on the Mitral Valve F.A.

[5] Barlow married Shelagh Cox in 1949 and they had two sons, Richard John and Clifford William who are medical consultants in dermatology and cardio-thoracic surgery respectively and working in the United Kingdom.