In no other part of the self is the tension between body and essence more tightly drawn than in the heart. That four-chambered organ, remarkably well understood as human components go, is often seen as basically a pump. Sophisticated and wonderfully adapted for its work, still -- a device for driving blood about the body on its critical passage through the lungs.And yet, as Albert Carter shows in the reflective and moving book "Our Human Hearts," part of a Kent State University Press series on literature and medicine, it remains for most of us what it has long been: the seat of special emotion; even more than the brain, the symbol of ongoing life . Even when Terri Schiavo's mind was long gone, she was still understood to be alive while her heart continued to beat.

An adjunct professor of social medicine at the University of North Carolina School of Medicine (not a physician; his doctorate is in comparative literature), Carter is the author of a previous book on a humanist's encounter with human anatomy . During a one-semester teaching/research appointment at the University of Montana at Missoula , he researched this book, largely at the International Heart Institute of Montana , based at St. Patrick Hospital and Health Sciences Center .

The book has three main elements. First, Carter's continuing education in the physiology (and pathology) of the heart from elite surgeons at the heart institute. Second, an exploration in several essays of the manifold meanings of "heart" in language, culture, society, and literature. Third, a rich and voice-filled presentation, based on extensive interviews, of four seriously ill heart patients.

In these encounters, the identity of the heart as seat of human essence is most literally felt. Michael is a 27-year-old athlete with a congenital valve defect that is to be repaired with the Ross procedure , a delicate and radical operation. Kay is a middle-age single woman with cardiomyopathy -- her heart muscle has been damaged by a virus -- who must learn to live with limitations and uncertain future. A third patient, a 51-year-old Episcopal priest, had angioplasty for severe coronary artery disease and was forced to rearrange his life and habits to fight the return of the illness. The last is a 91-year-old man with a history of stroke and hypertension, still holding on to life, prayerful and grateful.

It is startling to realize how imbued our view of human life is with the image of the heart. Carter discovers more than a hundred habitual tropes, which we use without a second thought, and lists many: strong-hearted, lionhearted, to be heartened, lighthearted, fainthearted, to lose heart, wholehearted, halfhearted, change of heart, his heart wasn't in it. These refer to the heart as the mainspring of courage or optimism. There are as many for the heart as the seat of wisdom, knowledge, and passion (both love and bitterness). None of these meanings have anything do with pumping.

If nothing else, "Our Human Hearts" would be a useful lay primer for the state of modern knowledge of the heart, and of modern medicine's ways of saving and healing it. But the heart of the book, as one might say, is the testimony of its four characters, and Carter's meditations on their words. They disclose the challenge to their assumptions about life and its value that comes from the knowledge of the vulnerability in their chests. Michael dreams of climbing Mount Kilimanjaro , in Tanzania, with his father once he recovers from his surgery. Kay fights to avoid bitterness and to treasure all that she can do, such as yoga, within limits. "I have my days of fear and anger," she says. "There are a lot of things I'd rather be doing, and a disease like this can rob you of your dreams. So you change some of your dreams."

One slight irritation is that the dialogues contain visual narrative markers that would seem impossible for the interviewer to remember without a videotape, which raises the unfortunate suspicion that imagination has crept, at least a little, into the reporting : "He shakes his head, eyebrows raised," or "He stops and smiles."

Despite the dangers they are in, the four patients have one thing in common: All seem to love life and find it worth fighting for, which makes the reader realize -- it's easy to forget -- how delicate and improbable our own lives are, what a heartbeat of eternity we occupy and usually take for granted.

© Copyright 2006 Globe Newspaper Company.