Very early in life, Joseph Loscalzo saw how merciless heart disease can be.

After his grandmother suffered a series of heart attacks, there was very little doctors could do. She was hospitalized and placed on bed rest, basically surviving through her final decades. Today’s modern medical tools and treatments didn’t exist.

Those painful memories stuck with Loscalzo for years — and inspired him. Decades later, as a renowned physician and researcher, he’s leading the charge to help patients in the exact opposite way his grandmother was treated: personally, and with precision.

Loscalzo is one of the leading minds behind the American Heart Association’s Institute for Precision Cardiovascular Medicine, which funds research to better understand the roots of each person’s very unique diagnosis. His work in this field, and many other contributions to fighting heart disease and stroke, earned him the organization’s Gold Heart award, the AHA’s top volunteer honor, last month.

Loscalzo still clearly recalls an important moment leading him toward precision medicine. He was very early in his medical career when he began questioning why an important clot-busting medication helped some heart attack patients, but not others.

“Seeing that kind of diversity in outcomes made me want to be more precise in sorting patients into response categories, and learn how to protect a person optimally before they have a heart attack,” said Loscalzo, chair and physician-in-chief in the Department of Medicine at Brigham and Women’s Hospital and the Hersey Professor of Theory and Practice of Physic at Harvard Medical School.

Precision medicine scrutinizes the impact of genes, environment and lifestyle on heart disease and stroke prevention and treatment — in hopes of answering the vexing question of why some medications and prevention tactics work for some people and not others.

Loscalzo points to common heart disease terms as examples.

“Heart failure is not one disease. It’s many, many different diseases, and heart attacks are not identical in the way they present for every patient,” said Loscalzo, who served as the editor of Circulation, the AHA’s principal scientific journal, for many years. “If you’re able to characterize an individual’s genetic makeup and the likelihood of their responding to a particular treatment, the better you’re able to treat those patients.”

From an early age, Loscalzo, the eldest of four children, was moved by a love of learning. After his dad died in 1969, when Loscalzo was 16, his great uncle Vincent, a pediatrician, guided him on everything from local politics to which subjects to study in college.

“He was very smart and self-effacing and had wonderful interpersonal skills,” Loscalzo recalled. “It was in his genetic makeup to be a problem solver and a comforter.”

Loscalzo attended college across the river from his family’s home in Camden, New Jersey, at the University of Pennsylvania, where he also completed medical and graduate school. There was never any question that science would be at the center of his studies. Lured by “the excitement of discovery and the honor of being able to help people when they are in the most vulnerable points in their lives,” a medical career soon followed.

Loscalzo’s twin desires to better serve patients and to help solve complex cardiovascular puzzles eventually led him closer to precision medicine.

A new approach was clearly needed, he said.

For example, he said, many physicians oversimplify their observations when it comes to high blood pressure treatment. When 100 people received a new drug that lowers blood pressure, on average it could reduce blood pressure slightly, Loscalzo said. But some patients will see huge gains, and others will hardly budge. The burning question remained: Why?

“Everyone will be expecting to get a good response, but that’s often not the case,” he said. “Once the medication is released to the general public, you’ll see a spread of responses.”

Solving that puzzle is why he was eager to take a prominent role in the AHA’s Institute for Precision Cardiovascular Medicine.

“Precision medicine can apply to every major cardiovascular disease — hypertension, heart failure, heart attack, stroke,” Loscalzo said. “I’m encouraged about the future. We may even get there in my lifetime, if not, certainly the lifetimes of my children and grandchildren.”