His major interest throughout has been the application of computer techniques to ECG interpretation. The work of his team has been adopted commercially and the University of Glasgow ECG interpretation program developed in his laboratory is currently used worldwide. He is particularly interested in differences in ECG appearances due to age, gender and ethnicity, and as a result, he has influenced international guidelines for the ECG definition of acute myocardial infarction. In addition, he has established an ECG Core Laboratory for handling ECGs recorded in national and international clinical trials and epidemiological studies.

Professor Macfarlane is a Fellow of many learned Societies, including the Royal Society of Edinburgh. In 2000, he was awarded a DSc on the basis of his contribution to research in his own field. He was also jointly awarded the 1998 Rijlant International Prize in Electrocardiology by the Belgian Royal Academy of Medicine. In January 2014, he was awarded a CBE for Services to Healthcare.