While exercising, the heart produces a protein called Heat Shock Protein 72, or HSP72, which protects cardiac muscles against injury in the event of a heart attack.

During a heart attack, the cardiac cells `commit suicide' at a rapid rate resulting in irreparable loss of vital tissues. HSP72 might check this process and save the cells from obeying a mysterious `suicide command' triggered by a genetic factor.

A recent study by University of Florida researchers reveal that less than a week's worth of walking, jogging or cycling can help the heart produce enough HSP72 to protect it against the damage done during a heart attack. ``We've done studies that indicate that as little as three days of exercise can provide protection,'' said ScottPowers, a professor in UF's department of exercise and sport sciences, in a paper published on the Internet today. Rats tested at UF showed that as few as five days of exercise produced almost the maximum amount of HSP72 that cells can hold.

``It raises the possibility that this could be true of humans, too, and we think that this is very exciting,'' Powers said.

HSP72 is in a family of proteins that form in the cells and protect organs in the body, such as the heart, against the type of extreme stress that a heart attack can cause. During stress, scientists believe, HSP72 can stabilize and refold damaged proteins, which is vital to preserving the heart if blood circulation is cut off.

``This heart shock protein prevents the cell from dying from stress that would kill cells that didn't have the same level of stress protein,'' Powers said.