3rd Degree Atrioventricular (AV) Block is a condition where the signals for the heart rate from the sinus node are not received or allowed through the AV Node.  

This is usually a result of scarring/fibrosis of the AV Node where the conductive tissue is no longer allowing the signals to travel through this region.  

This results in a rhythm called a ventricular escape rhythm that is enough to keep the patient alive, but is very slow (typically 30-40 beats per minute).  Affected patients often collapse and have extreme exercise intolerance because their heart rates are not appropriate for higher activity levels.  

This condition is typically incurable; however, this can be treated with a pacemaker, which ensures the heart rate never drops below the minimum programmed value.  

Until a pacemaker can be implanted, medications can be attempted to increase the ventricular rate slightly.  

These medications are typically effective for only a short time, if at all.