An acute myocardial infarction (heart attack) occurs when an area of the heart muscle dies or is damaged due to an inadequate supply of oxygen. A blood clot forms in one of the coronary arteries, the blood vessels that supply blood to the heart. This clot prevents blood, and consequently, oxygen from reaching the heart cells in that area, leading to their death.

Sometimes the arteries that feed into the heart narrow gradually over time, as a result of a cumulative accumulation of an obstruction (made up of fatty material). The amount of blood that can flow through the artery, and reach the heart, is reduced. Because blood carries oxygen, the heart is not able to receive the amount of oxygen it needs. Chronic disease often leads to heart attack, when a blood clot forms at the site where the artery is narrowed.

Until a few years ago, scientists thought that it was impossible to repair a damaged heart. The discovery of cardiac (heart) stem cells, just over three years ago, opened up new possibilities to use stem cells to repair hearts that have been injured through heart attacks (acute myocardial infarction) or chronic disease (chronic coronary artery disease). Several studies using animal models of heart disease suggest that transplanting bone marrow stem cells into injured hearts can indeed partially repair these hearts. As a result, there are currently many ongoing clinical trials of bone marrow transplants to treat heart disease, particularly heart attacks (acute myocardial infarction).

Generally speaking, in these trials patients who have suffered a heart attack are given preparations of their own bone marrow stem cells – these are called autologous transplants. These trials have demonstrated that this treatment is safe and have recorded relative improvements in heart function. However, many scientists feel that the findings are not consistent and many questions remain as to their clinical relevance and long-term effects. Consequently, scientists feel that continued laboratory research, using animal models and cells grown in the laboratory, are needed, in order to advance in the clinical trials.

Some of the questions scientists are trying to answer include understanding exactly which cells in the bone marrow (or in the blood) are having an effect on the damaged heart. Scientists are also studying whether the bone marrow stem cells become new heart muscle cells and/or blood vessel cells, whether they stop existing heart cells from dying, or whether they release substances that stimulate the existing heart stem cells to divide and replace those that have died.