Cancer that begins in the heart is most often sarcoma, a type of cancer that originates in the soft tissues of the body. Heart cancer (malignant primary cardiac tumor) is extremely rare. One study reviewed more than 12,000 autopsies and found only seven people with primary cardiac tumor. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.