Original sentence: A "heart attack", or myocardial infarction, happens when there is an interruption of blood supply to cardiac tissue through the coronary arteries, resulting in death of cardiac tissue.Actually a "heart attack" and a "cardiac arrest" aren't the same thing.Conversely, a "cardiac arrest" can have causes other than a myocardial infarction - such as an arrythmia.Depending on the location and extent of damage, this may, or may not, cause a cardiac arrest.There was an episode due to be shown on 12 May 1994, however this was replaced with an extended 9 o'clock news programme due to the sudden death of Labour leader John Smith, who ironically died from a heart attack (also known as a cardiac arrest)
Edited sentence: There was an episode due to be shown on 12 May 1994, however this was replaced with an extended 9 o'clock news programme due to the sudden death of Labour leader John Smith