This is an incomplete and misleading bit of information from these “researchers.” Anybody with Atrial Fibrillation knows that chocolate (probably due to its caffeine content) can easily throw one’s heart into A-fib which, if it gets into an uncontrolled run-away heart-rate, can be dangerous and even lead to a heart attack or stroke.
Unless they include this information in their research (haven’t read the full story, don’t have time), it is potentially unhelpful or even dangerous info—could be harmful for people to automatically assume eating a lot of chocolate will help their heart.
They’re talking about 2.5 ozs, not ‘a lot.’ But every person should know what’s good for his/her heart and overall health, and a patient with a known heart condition should definitely consult with the doc before embarking on any variation to the diet.