At what percentage of blockage do cardiologists perform a stent procedure?

Varies: Varies but generally over 70%. Depends upon symptoms and if another test such as a perfusion scan shows ischemia in the vascular territory supplied by the artery. There is not only science but an art involved in this. Medications are getting better and better so often coronary artery disease is treated with medication, not stenting or bypass.

70%: Or greater. Sometimes fractional flow reserve is used to ensure a blockage is hemodynamically significant.

Depends: Most interventional cardiologists would stent lesions > 70%. However this depends also on patients symptoms and other evidence of significance of blockage. Visual estimation of severity of lesion is not the most reliable method. There are other ways to assess severity of lesions. Most however would not stent lesions less than 40 to 50%.