Public defibrillators can now be found in growing number of places, but a new study suggests parts of downtown Toronto are underserved.

Defibrillators are used to shock the heart back to its normal rhythm and are credited with saving many lives.

But according to a University of Toronto engineering professor there are public places in our city that need these life-saving devices.

Timothy Chan developed a mathematical formula that "tries to identify geographies where there are clusters of cardiac arrests that are close together and basically where there are no existing defibrillators."

There are 10 downtown areas Chan says are hot spots - including Queen and Bay, Dundas and Spadina as well as Jarvis and Gerrard.   Currently no one regulates where defibrillators are installed in Ontario.

Chan wants his study to change that.

Chan says in the denser parts of downtown Toronto, people shouldn't have to walk father than 100 metres to get to a defibrillator