what is lead?

Since your question is under "Heart Diseases" I'm assuming that this is what you are looking for.

"A lead is a special wire that delivers energy from a pacemaker or implantable cardioverter defibrillator (ICD) to the heart muscle."

I hope that answers your question. However if you are speaking of lead as in the toxic metal, I have also included a link that explains that as well.

I hope this helps!

Michelle

Lead (chemical symbol: Pb) is a heavy metallic element. Like other heavy metals, such as mercury, and cadmium, it has adverse health effects on humans, particularly children, and even small amounts can impair them intellectually.