The heart can be stopped following trauma at a very specific point in its cycle. This is called commotio cordis.

The body region of interest here is the precordium, the area of the chest wall lying directly above the heart.

The precordium is a shield, made of the ribs and their muscles, which inflate and deflate our chest. Further swaddling is provided by the pericardium, a sac of membranes interposed with cuffs of shock-absorbing fat and fluid.

Impacts on these region may trigger commotio cordis. However the timing window for this to happen is small, as it must occur in a very specific section of the heart’s electrical rhythm, making the likelihood around 1/100.

This makes commotio cordis a rarity, but nonetheless significant. The disruption of the cardiac cycle here can lead to a severe, potentially lethal rhythmic disorder. This is known as ventricular fibrillation. Medical teams must act quickly, using chest compressions, adrenaline and resuscitation with a defibrillator to restore a normal cardiac rhythm.

In some situations, blows in this area can actually restart a heart.

Historically, part of the algorithm for treating a patient in cardiac arrest was to first strike the precordium once using the base of a clenched fist. This is called a precordial thump. The reason why this could work is the same behind commotio cordis: mechanical energy that turns into tiny electrical currents. However some studies have found no benefit for its use at all.

References

• https://theconversation.com/a-blow-to-the-heart-can-kill-you-or-bring-you-back-to-life-224197