How a heartbeat carries its signal
Each heartbeat depends on an electrical impulse moving from one heart cell to the next in an orderly sequence. In working heart muscle, sodium channels act like tiny gates: when they open, sodium rushes into a cell and helps trigger the rapid electrical change that lets the impulse spread.
Cocaine can plug these channels, making it harder for the impulse to travel through heart tissue. This is a direct effect on the heart’s electrical wiring—not just a consequence of feeling stimulated or having a faster pulse.
When conduction slows, timing can break down
If enough channels are blocked, the impulse spreads more slowly and less reliably. Different parts of the heart may then activate out of step. On an electrocardiogram, clinicians may see signs of slowed conduction, such as a widened QRS complex—the portion of the tracing that reflects the ventricles, the heart’s main pumping chambers, activating.
A disrupted signal can produce an arrhythmia, meaning an abnormal heart rhythm. Some rhythms are merely irregular; others prevent the heart from pumping blood effectively and can become life-threatening.
More than one strain on the heart
Cocaine can also raise the body’s levels of stress chemicals, increasing the heart’s workload and oxygen demand. Those effects can occur alongside sodium-channel blockade, so the heart may be working harder while its electrical signals are becoming less coordinated.
That combination helps explain why a person’s pulse alone cannot show how safe the heart’s rhythm is. The danger is not simply that the heart beats quickly: the electrical impulse that organizes each beat can itself be disrupted.
