In a phase 1 and 2 trial in which mesenchymal stem cells (MSCs), bone marrow mononuclear cells (BMCs), or placebo was used to treat patients with ischaemic cardiomyopathy (n = 65), serious adverse events occurred at a similar rate in all three groups. After 1 year, patients treated with MSCs or BMCs had improved Minnesota Living With Heart Failure scores; this improvement was not seen with placebo. Patients treated with MSCs—but not BMCs or placebo—also had improvements in the 6-minute walk distance, decreased infarct size, and improved regional myocardial function relative to baseline measurements.