It's caused by sudden stress (e.g. bereavement, illness) which leads to weakening of the heart muscle, causing the heart to bulge out at the apex. It's named 'tako-tsubo' because the heart starts to resemble a round vessel used in Japan to catch octopuses.
I dont know about bulging but when I experienced my first break up in the 20s, I literally felt a hole in my heart for many days. It was a surreal experience, for some reason my mind was just telling me that there is nothing there where my heart should be.