One theory on the limited results for heart failure is that patients' bone marrow cells are not retained in the heart for a long enough time.
So in the new study, German researchers first "pre-treated" patients with so-called shock wave therapy, which applies high-dose ultrasound to the chest. For patients, the experience is similar to having a diagnostic ultrasound of the heart, said senior researcher Dr. Andreas Zeiher, of Goethe University in Frankfurt.
One day after the shock wave therapy, patients' hearts were infused with a dose of their own bone marrow cells.
The idea, Zeiher explained, is that the shock waves might spur the heart to churn out chemicals that attract more bone marrow cells to the damaged portion of heart muscle.
After four months, his team found, there was a 3 percent increase in the patients' left ventricular ejection fraction -- the percentage of blood pushed out of the heart with each contraction.
That's a "decent" improvement, said Dr. Eduardo Marban, director of the Cedars-Sinai Heart Institute in Los Angeles. And it's possible it could translate into long-term benefits -- like a lower risk of a repeat heart attack or longer life, according to Marban.