Pope John Paul I died only 33 days after his papal election due to an apparent myocardial infarction, resulting in the first year of three popes since 1605.

Pope John Paul I was head of the Catholic Church and sovereign of the Vatican City State from 26 August 1978 until his death 33 days later. His reign is among the shortest in papal history, giving rise to the most recent year of three popes—the first since 1605. John Paul I remains the most recent Italian-born pope, the last in a succession of such popes that started with Clement VII in 1523.

A conclave was held on 25 and 26 August 1978 to elect a new pope to succeed Paul VI, who had died on 6 August 1978. Of the 114 eligible cardinal electors, all but three attended. On the fourth ballot, the conclave elected Cardinal Albino Luciani, the patriarch of Venice. After accepting his election, he took the name John Paul I.

A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops in one of the coronary arteries of the heart, causing infarction to the heart muscle. The most common symptom is retrosternal chest pain or discomfort that classically radiates to the left shoulder, arm, or jaw. The pain may occasionally feel like heartburn. This is the dangerous type of acute coronary syndrome.

A year of three popes is a year when the College of Cardinals of the Catholic Church is required to elect two new popes within the same calendar year, in particular the last instance in 1978. Such a year has historically occurred when a newly elected pope dies very early into his papacy. This results in the Catholic Church being led by three different popes during the same calendar year. In one instance, in 1276, there was a year of four popes.