Previous work in Canada and Australia has identified a strong relationship between numbers of heart attack deaths and temperature in conditions of extreme heat or cold. In addition, the calculation of a “pool of susceptibles” has provided a partial explanation for the varying strength of the relationship from season to season and from year to year. Recent work on cardiovascular morbidity in northeastern France has identified the day of the week as an additional significant factor in determining the number of reported cases and finds that this effect is particularly significant for younger patients. Monday was cited as the day with the highest heart attack morbidity. The current work re-examines both Canadian and Australian data from the 1980's for possible day of week effects. In all cases, five years of daily death data were available divided by gender and into those over and under age 65. For the Canadian cities, two overlapping five year periods were examined, 1983-1987 and 1987-1991.

In Brisbane, Australia, 1980-1984, the highest number of heart attack deaths occurred on Monday for both men and women over 65, but on Saturday for men under 65 and on Sunday for younger women. In Montreal, Canada, from 1983-87 the most deaths occurred on Monday for all gender/age groups except on Saturday for Women over 65. From 1987-91 most deaths occurred on Tuesday for all gender/age groups except on Sunday for Women Over 65.

In Toronto from 1983-87 the most deaths occurred on Saturday for all gender/age groups, except for men under age 65 for whom Sunday was the modal day. In the later time period, men over 65 died most often on Fridays while Saturday was the mode for the rest of the population. In Vancouver, Friday was the modal day for all gender/age groups from 1983-1987, but in the later time period each group had a different modal day, Thursday for men over 65, Friday for older women, Saturday for younger women and Sunday for men under 65.

In Winnipeg the most deaths occurred on Thursday for men over 65 in the first time period and both elderly men and women in the second period. Other modes were scattered from Wednesday to Sunday for different age/gender groups in the two time periods. A possible explanation for this great diversity lies in the relatively small population of Winnipeg and the far larger number of days without any heart attack deaths at all.

Overall, it is concluded that, at the scale of five year time blocks, heart attack deaths are not evenly distributed throughout the week, although the weekends and Friday often have more deaths per day than Monday. An investigation of individual years and particular seasons of the year may help to explain some of the patterns described.