Why did Light kill people with heart attack?
He wanted people to see that these deaths were not a coincidence. If some died from cancer, others from gunshots, and a few from heart attacks- then it becomes harder to attribute these all to one person. So, Light made it uniform. If someone randomly died of a heart attack- and they were a criminal, you could be sure that Kira, god of the new world, had passed judgement. edit: soccersarah hit the nail on the head when saying why it was specifically a heart attack, instead of anything else. It was the default choice. Also, I forgot to mention that Light wanted to keep the fact that he could kill people in other ways a secret. This came quite in handy when he was dealing with Ray Penbar and his wife.
