No Electrical Activity

Asystole occurs when there's no cardiac electrical activity in the heart. Naturally, there is also no pulse.

Always check for a pulse!
If a patient is in true asystole, they will look - well- dead. That said, it's still important to confirm that there's no pulse.

Immediately start CPR! For asystole, defibrillation is not performed.

In Canada and the United States, treatment is based on the AHA/HSF Advanced Cardiac Life Support Cardiac Arrest algorithm:

Early Epinephrine
Epinephrine 1mg IV/IO q3-5mins.
Hs and Ts
Treat underlying condition(s).

For more information, check out the AHA ACLS Cardiac Arrest pathway here:

AHA Adult Cardiac Arrest Algorithm, VF/pVT Pathway

Disconnected ECG Cable

Because the body naturally has some electrical activity for some time after cardiac standstill, these readings can be captured by the ECG machine so it's rare for an ECG reading to be truly "flat line." Unless the cardiac monitor is doing some impressive filtering, a perfectly flat ECG line - accompanied by a patient whose alive and awake - is likely to be a disconnected ECG cable.