On a recent trip to east Africa, ET's Mary Hart came face to face with mountain gorillas -- and in this Web exclusive video blog, she tells us, "Nothing in my entire life had ever prepared me. My heart just about beat out of my chest."

Mary made what she calls "the journey of a lifetime" with a group of her closest friends to trek into Virunga National Park to visit the rare high mountain gorillas of Rwanda.

"Then we came around a bend and I could hardly believe my eyes," Mary continues. "We had come upon an entire family of spectacular apes. They're so rare. It's believed there are only about 700 in existence and we were right in their backyard."

It was a 3-1/2 hour trek into the Virunga Higlands -- between Rwanda and the Congo -- where one year ago six of the gorillas were brutally shot and killed. The shocking crime is the subject of "Explorer: Gorilla Murders," airing Sept. 16th on the National Geographic Channel.

For more on Mary's trip to Africa, tune in to Tuesday night's ET!