Viral Heart Disease
From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
The Viral Heart Disease is a deadly virus that Future Son Goku contracts in November or December of 766 Age and dies from in Future Trunks' alternate timeline. Six months following his death, the Artificial Humans appear and murder all of the Z Warriors with the exception of Future Son Gohan, thus sparking the events of The History of Trunks as well as the Trunks, Androids, and Cell sagas. The specific name of the virus is never stated nor how he got it.
In the main timeline, Future Trunks arrived from the future and gave Son Goku the Vaccine to the Viral Heart Disease. (The Viral Heart Disease was incurable in the alternate timeline, but a cure was developed soon after Future Goku had died). His presence in the past, however, caused history as he knows it to change drastically. One major change was that Goku did not contract the Viral Heart Disease when he was originally supposed to, but instead it appeared six months later during his fight against Artificial Human No. 19 in May of 767 Age. Goku was saved from death by Vegeta and taken home to receive the Vaccine. A few days later, the Viral Heart Disease was successfully cured and Goku re-joined the fight against the Artificial Humans and the newest threat, Cell.
It is never explained why Goku contracted the Viral Heart Disease a year after his alternate timeline counterpart, although a possible explanation is that Goku, knowing of the Artificial Humans' arrival, was at home training whereas Future Goku, thinking that all was well, was out having fun with his family and contracted the Viral Heart Disease earlier. Main timeline Goku appeared to have contracted the Viral Heart Disease while in the city where the Artificial Humans first appeared, as he was noticably exhausted after merely flying away from the city – justifying that he did not catch it while training for the upcoming fight against the Artificial Humans – since Goku's house was in the middle of nowhere.
The Viral Heart Disease appeared in Dragon Ball Z: Budokai, Dragon Ball Z: Budokai 2, Dragon Ball Z: Budokai 3, and Dragon Ball Z: Infinite World as a capsule that could only be used by equipping it in the "Custom" menu of the character's selection screen. It takes up three tray slots and causes the health of both the user and opponent to deplete continuously until only half of their last health bar is left. The user and opponent can avoid taking damage by equipping the Vaccine capsule which nullifies the Viral Heart Disease's effect and take up one tray slot.
It is named Heart Virus in Dragon Ball Z: Legendary Super Warriors.