Hi, I don't want to be an asshole but this is not quite true and I would like to correct this. Sorry to disturb. The first thing is to make a distinction between heart attack and cardiac arrest.

During a heart attack, a plaque ruptures and blocks the coronary arteries and cardiac tissue dies. The heart keeps on beating despite this. During massive heart attacks, the blockage can be so severe that it may cause a fatal arrhythmia (cardiac arrest).

The Cough CPR is has been shown to not be useful outside hospital monitorization. Is used mainly during cardiac catheterization to stabilize the initial seconds of a sudden arrhythmia. It doesn't work for all people despite these controlled conditions. 

The pressure that coughing exerts on the vasculature is not enough to prevent or stop a cardiac arrest. One should look for attention immediately. Is a lot more useful to recommend people to have a speed dial number on their cellphones or computers.

http://www.heart.org/HEARTORG/Conditions/More/CardiacArrest/Cough-CPR_UCM_432380_Article.jsp#.Wg_jo9LiYWo

https://health.clevelandclinic.org/2013/07/can-you-cough-away-a-heart-attack/