Anything done in pectore is done literally "in the breast"; such as, the designation of a cardinal by a pope without public announcement. The designation is said to be in pectore.

When the pope names new cardinals, sometimes he will announce that one or more are named in pectore; that is, "secretly". The name, or names, are not announced publicly and only the pope knows the name and even the new cardinal is aware that he has been chosen. Usually, it is not recorded anywhere.

During times of political hostilities, popes used in pectore

As anti-Catholic hostility among various governments became common, in pectore appointments became more common during the late 18th and 19th centuries.

Pope Pius VII created eleven cardinals in pectore; despite the anti-Church hostility of the French Revolution, all of them were eventually published, as were Pope Leo XII's three in pectore appointments.

The outbreak of major revolutions in Europe during the late 1820s caused the proportion of in pectore appointments to all cardinal appointments to rise dramatically: Pope Pius VIII created thirteen cardinals, but only five of them were ever published, while Pope Gregory XVI created as many as twenty-eight cardinals out of a total of eighty in pectore; of which five were unpublished.

Also, creati et reservati in pectore is a term which means, "create cardinals without declaring their names"; that is, "in the chest".