The post you are reporting:
Bob, the chart title is "Acute myocardial infarction admissions", giving a clue as to the type of heart attack being reported on. If you matched this chart wih one showing the growth in use of statins, beta-blockers, aspirin etc., you may see the same trend, but in reverse.
Ergo, there's much more "heading off at the pass" due to better diagnosis and treatment before heart attacks get acute. Also ambulances now carry better equipment to deal with heart problems and paramedics do a terrific job in sorting most out before they get serious. Furthermore, patients don't have to wait for stents to be fitted as they did years ago, and that helps avoid heart problems becoming major.
So, I would say it is a coincidence with regard smoking bans because they don't actually stop anyone from smoking, just going to the pub! On that basis, it would be interesting to see a graph of pub closures since the introduction of the smoking ban.