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The evidence that the heart can regenerate muscle cells and the possible existence of cardiac stem cells raise hope that it may be possible one day to induce cardiac stem cells to migrate to a damaged area of the heart to repair it with new cells.

In an analysis of the hearts of patients who died after having a heart attack, researchers detected signs that heart muscle cells called myocytes continued to divide after a heart attack.

The researchers examined the hearts of 13 people who died within a few days of having a heart attack and compared them with 10 normal hearts. The researchers screened the tissue for the expression of Ki-67, a protein that is present only in dividing cells.

The major finding of the study is that the heart's capacity to regenerate myocytes increases immediately after a heart attack.

The investigators report that Ki-67 was present in many of the cells of the diseased hearts. Compared with normal hearts, the expression of the protein was 84 times greater in tissue immediately surrounding damaged heart tissue and 28 times greater in other heart tissue.

The researchers also detected other cell structures linked to the cell-division process in the hearts of people who had died from a heart attack.

The newly formed heart muscle cells may arise from stem cells--immature cells that specialize to form other types of cells--which reside in the heart. Cardiac stem cells have not been identified, but similar cells are present in the brain.

The heart clearly needs help to deal with the massive injury caused by a major heart attack. Help may be on the way, as animal studies have shown that stem cells taken from adult bone marrow can regenerate heart cells after a heart attack.

The New England Journal of Medicine (June 7, 2001; 344: 1750-1757, 1785-1787) noted that the study has shown the mysterious processes by which the body regenerates, and the body does not yield its secrets easily.