Growing up, my best friend was my grandfather, who was always smiling and happy. He was a candy-maker, and some of my best memories are of making fudge with him. But all that candy took a toll, and at age 69, he had a heart attack. After that, everything changed. He cried a lot, seemed unhappy, couldn’t sleep, and was eventually diagnosed with depression. I didn’t know it at the time, but depression is three times more common in people following a heart attack, according to research.