Sulu suffering from heart flutter
A heart flutter was an abnormal rhythm that occurred in the atria or ventricles of the heart. Cordrazine was used to treat the condition. (TOS: "The City on the Edge of Forever")
In 2267, Doctor Leonard McCoy diagnosed a reviving Khan Noonien Singh with heart flutter and warned that he could die in seconds if they didn't get him out of his cryogenic stasis. (TOS: "Space Seed")
Later that year, Hikaru Sulu was diagnosed with a heart flutter after a technical malfunction on the bridge of the USS Enterprise caused his console to overload and explode in his face. (TOS: "The City on the Edge of Forever")