Karoushi (かろうし) is a relatively new colloquialism created from three kanji meaning to die from overworking (stress related heart failure or otherwise). The first character, ka, means to exceed or overdo. The second character, rou (long O), is used for laboring or toiling (and also used in the words for trouble, pain, and work-related injury or death: roudousaigai). The third, shi is used for death.
According to Japan's Ministry of Health 143 people died from karoushi in the year ending March of 2002 (up nearly 70% over the previous year). The great majority were men, most in their 40s and 50s (only 10 were women); Many of the karoushi were stress related (fatique, heart failure), while 31 were suicides.
Numbers from Asahi Shimbun