In baseball, 'heat' is slang for fastball, so 'high heat' is a high fastball.
Fastball
The fastball.
Bob Gibson has the 7th fastest fastball in major league baseball history. His fastest fastball was clocked at 96 miles per hour.
The fastball is the pitch most thrown and most hit in baseball.
Fastball, slider, curve ball, change up. Other pitches include the splitter (split finger fastball) and knuckleball.
A split-finger fastball or splitter is a pitch in baseball and a variant of the straight fastball. It is named after the technique of putting the index and middle finger on different sides of the ball, or "splitting" them. When thrown hard, it appears to be a fastball to the batter, but suddenly "drops off the table" towards home plate
Fastball is a noun.
A baseball pros fastball is on average 92 mph
The most accurate pitch in baseball is the 4-seam fastball. You can throw a 4-seam fastball by: Placing your index finger and middle finger comfortably apart from each other across the seams where the seams are farthest apart from each other. Then, throw it as if you were playing catch.
It's difficult to attribute the invention of the fastball to a single person, as it has likely been used by players since the early days of baseball. However, pitchers like Amos Rusie and Christy Mathewson are known for popularizing and perfecting the pitch in the late 19th and early 20th centuries.
An average fastball for a senior at the college level is 90 mph.