Yes, “heart” is a common noun. It refers to a general category, the organ that pumps blood through your body, rather than naming one specific, unique entity. You write it in lowercase unless it starts a sentence.
Why “Heart” Counts as a Common Noun
Common nouns are the everyday names we give to people, animals, places, and things. They refer to a general type rather than a specific individual. “Heart” fits this definition perfectly because it names a body part that every person has. As the University of Arkansas explains in its grammar resources, “A heart beats 74 times a minute” doesn’t refer to one particular heart; it refers to the body part in general.
Proper nouns, by contrast, are the special names we give to specific people, places, or things. They always start with a capital letter. “London” is a proper noun because it names one specific city. “City” is a common noun because it could refer to any city. In the same way, “heart” is common because it could refer to any heart, not one in particular.
How “Heart” Works in Sentences
Oxford Learner’s Dictionaries classifies “heart” as a countable noun across most of its meanings. This is typical of common nouns: you can say “a heart,” “two hearts,” or “many hearts.” Here are the main ways the word gets used.
As a body part: “I could feel my heart pounding.” “He has a bad heart.” In these sentences, “heart” names the physical organ in someone’s chest.
As a metaphor for emotions: “Her heart filled with joy.” “Have a heart! Can’t you see he needs help?” English speakers treat the heart as the symbolic home of feelings, especially love and compassion. Even in this figurative sense, it remains a common noun.
As the center of something: “A quiet hotel in the very heart of the city.” “The report went to the heart of the government’s dilemma.” Here “heart” means the core or most important part, and it stays lowercase and common.
As a shape or suit in cards: A red heart symbol, or the hearts suit in a deck of cards. In card games, “hearts” can also function as an uncountable noun when referring to the suit itself.
When “Heart” Gets Capitalized
You capitalize “heart” at the start of a sentence, but that doesn’t make it a proper noun. Capitalization at the beginning of a sentence is just a rule of punctuation. The word itself stays common.
The only situation where “heart” might look like a proper noun is when it appears as part of a proper name, like the American Heart Association or Sacred Heart University. In those cases, “Heart” is capitalized because it’s part of a specific name for a specific organization. On its own, though, “heart” is always common.
All Body Parts Follow the Same Rule
Every body part in English is a common noun: brain, lung, kidney, liver, hand, foot. None of them name a unique, one-of-a-kind thing. They all describe a general category of thing that many people (or animals) have. So if you’re ever unsure whether a body part is common or proper, the answer is always common.