Melville, N.Y. ? The human heart undergoes an inevitable – and inexplicable – shrinkage at the half-century mark, a phenomenon that its discoverer is calling the “age 50 effect,” a mysterious development that affects both genders.

“This is the first time that this kind of narrow time window has emerged for such a dramatic change,” said Dr. Nathaniel Reichek, director of research and education at St. Francis Hospital, The Heart Center in Roslyn, N.Y.

While other medical investigators, including researchers with the Framingham Heart Study in Massachusetts and the Mesa Study at Johns Hopkins University, have uncovered similar evidence, Reichek and his team have defined it, and timed chronologically when it occurs.

“It has been recognized for some time that the heart chambers get smaller with age, but what pops out in this work is that there is an inflection point,” he said of the 50-year mark, “where rapidly occurring change occurs.”

Reichek and colleagues conducted imaging studies – cardiac ultrasound and EKG to rule out participants with silent heart disorders. They further ruled out people with diabetes, mild high blood pressure, obesity and other problems that potentially could confound tracing how the normal heart ages.

The 218 participants in the research – all residents of Long Island and New York City – were defined by Reichek as “genuinely normal” because they were free of illnesses, especially chronic cardiac problems. The actual study of the heart involved magnetic resonance imaging – MRI – exams. Participants ranged from their 20s to late 80s.

Yet, at the moment, Reichek’s discovery of mid-century cardiac shrinkage seems to have raised more questions than answers.

Can exercise blunt or even reverse the effects of cardiac shrinkage? Why age 50? Why not 40 or 60? Does substantial change – a shrinkage of at least 16 percent – lay the foundation for heart failure later in life?

“Those are all very good questions, but we don’t have the answers at this time,” Reichek said Tuesday. Hence, his study is hunting down the underlying causes.

What he has found so far suggests that blood pressure rises as the heart loses size. An age-related increase in blood pressure has been recognized by the American Heart Association and the American College of Cardiology, which recommends that adults, especially those 50 and older, have their blood pressure routinely checked by a health care professional.

Reichek also found that even though the heart shrinks in both men and women, certain gender-specific anomalies remain. The right ventricle in men, for example, is generally larger than in women. Despite overall heart shrinkage in both genders, the sex difference in ventricle size persists.

Dr. Nieca Goldberg, medical director of the women’s heart program at New York University Medical Center in Manhattan, wonders what the findings mean.

“It’s always better for the heart to be smaller than to be enlarged,” said Goldberg pointing to several cardiac conditions marked by an oversized heart, such as untreated hypertension and congestive heart failure. Excessive alcohol consumption “can cause enlargement,” Goldberg added. “Everybody associates it with heart health. But it’s only moderate amounts that are healthy.”

Still, she thinks Reichek may have opened a window on new questions about the aging heart. “It is an interesting finding, but I’d like to see more research,” she said.