Heartstoppers[edit]
At two points during the contestant's campaign, a "heartstopper" event took place. These were designed to raise the heart rate (coming face to face with an alligator or a hive of bees, a large pendulum swinging just overhead, having McEnroe serve tennis balls at the contestant's head, etc.). Precautions were taken to ensure the contestant's safety during these events, such as a pane of heavy plastic being set just in front of his/her face as McEnroe served. If the contestant could endure the event for 15 seconds, or 20 seconds in the Korean version of the show, the event would end. If he/she went over the redline rate, the event would continue until the heart rate was under control, and he/she would lose money at the rate for the previously answered question. In the Korean version, the host is responsible for initiating the heartstopper by saying, simply enough, "start the heartstopper," at which point the countdown begins. On the US version, if a contestant is redlining the heartstopper is not officially over until the contestant lowers their heart rate back into the "safe zone".
Stabilize[edit]
After answering the $15,000 question correctly (for a potential prize of $35,000), the contestant earned the chance to "stabilize". Once during the rest of the game, he/she could exercise this option after a correct answer; if he/she missed a question or received three warnings, he/she would leave with the money won up to the "stabilize" point. However, if the contestant redlined in the interim and went below the stabilized amount, the stabilized amount would fall and match the current prize amount.
In the UK version of the show, a contestant was required to stabilize after correctly answering the fifth question if he/she had not yet done so by that point.
Countermeasure Rule[edit]
Contestants were required to stay alert during the game at all times. If a contestant tried to close his/her eyes or perform some other task in an attempt to lower the heart rate, McEnroe gave a warning. Three warnings would end the game (contestants can still leave with their stabilized amount). The latter never happened, though one contestant on the US show was warned twice and almost disqualified for the above actions. On the first episode, one contestant closed her eyes for the entire time on the one heartstopper she reached and was not given a warning. In the Korean version, that warning rule only applies in heartstoppers.