To say Heifetz was a rare virtuoso is like calling Einstein a genius. Heifetz is probably the greatest violinist ever recorded. You can hear that in the above link. He moves up and down scale-like passages with felicity; the notes sound clearly and distinctly and the dynamics are pure despite the speed of it all.
Another performance so good it’s almost ridiculous: Beethoven, Violin Concerto in D, 3rd Movement. Here Heifetz takes a grand, majestic theme and milks it for all it is worth. His high notes don’t sound shrill or forced. The fluidity he achieves all throughout complements the softer tone and dynamics he uses at key moments. I imagine it is easy to be too exuberant with this piece and pound away at the main theme, leaving the rest as filler. Heifetz preserves the tension and drama that marks nearly all of Beethoven and makes it look like it was the simplest thing in the world.