Medical researchers said they successfully used a genetically engineered protein developed by Genentech Inc., to help heart patients grow blood vessels around potentially lethal blockages in their coronary arteries. In a study involving 15 subjects, researchers found evidence that the protein, eager vascular endothelial growth factor, or VEGF, promoted blood improved symptoms in at least five patients. Thirteen of the patients reported improved symptoms such as reduced chest pain, researchers said. The study conducted by Timothy Henry of the Hennepin County Medical Center and his colleagues is small, but it is the first from a corporate research program to demonstrate that a biotech therapy can promote blood-vessel growth in the heart.