Before the shots of espresso would cause a heart attack and kill you you'd need to consume at least 500 grams of caffeine which is the toxic level of caffeine.
And each shot of espresso contains 40 to 50 grams of caffeine which is higher than regular coffee so it would take around 10 shots of espresso before it causes a heart attack.
It doesn't mean that the espresso would actually kill you once you reach the 500 grams of caffeine and have a heart attack because if you get medical attention for the heart attack you can sometimes be saved.
But you can expect a heart attack after 10 shots of espresso if drank too soon so avoid drinking more than a few shots of espresso throughout the day to avoid health problems.
If you already have heart disease then the heart attack could happen with less than 10 shots of espresso.