What would life expectancy be in the western world in the absence of Ischemic heart disease?
This paper from 1991 is intervention-based, so it reports the effects of behavior modification on lifespan in people who turned 35 in 1990.  The authors report the gains for each individual behavior and then say:


  Eliminating coronary heart disease mortality is estimated to extend the average life expectancy of a 35-year-old man by 3.1 years and a 35-year-old woman by 3.3 years


Which they feel is a modest increase but I rather disagree.  This report estimates the that reduction in death due to heart disease of over 50% between 1950 and 1995 gained around 3.5 years, although most of that is probably due to better medical treatments.  This 2004 study used 1998 data from the UK and estimated that:


  The average gain in life expectancy from the elimination of cardiovascular disease risk as a cause of death was 4.0 years for all the 35 year-old men in the sample (n = 24), and 1.8 years for all the 35 year-old women in the sample (n = 32).


Although I would note the low sample size.  I didn't expect to find much, so I was surprised to find these... and with similar results!  One big issue is that a lot of the more recent research has focused on smoking, weight/BMI, and blood pressure reduction, rather than all IHD/CHD/CAD; I found tons of those.  As a side note, simply reducing TV watching to less than two hours a day can lead to a gain of almost 1.5 years.