Puppies born June through August have the highest risk of developing heart disease says a study by researchers at the Perelman School of Medicine at the University of Pennsylvania. They feel that air pollution may be the cause. Their study showed that breeds that are already prone to heart disease were not affected by their birth month but breeds that are not prone to heart disease were affected.
Puppies born in July had the highest risk, at 74%. The researchers found that the risk for heart disease existed for both dogs and humans. Outside air pollution during pregnancy and at the time of birth appears to play a role in later development of heart disease. They coordinated their findings with research that had been conducted on people and found similarities. While the connection between outside air pollution is suspect, it has not been completely proven to be the cause but is a strong suspect.
I would like to see further research to see if the risk is greater in cities and countries where there is greater or less air pollution and compare it with the current findings. In the meantime, for those dogs born within the suspected time-frame, it would benefit dog owners to make sure that they take their dogs for annual checkups and watch for signs of heart issues. Also, diligent breeders could avoid having puppies born in the summer.