A study from the Johns Hopkins University School of Medicine, published online in the Journal of Clinical Investigation, found that sildenafil appears to strengthen RGS2, a protein essential in protecting the heart"s blood-pumping function. The hearts of mice, engineered to lack RGS2, expanded in weight by 90% and died of heart failure almost halfway through the test. But, in the animals with RGS2, the hypertrophy was delayed, growing by only 30%. After the researchers gave Viagra to the mice with RGS2, their hearts had stronger contractions and produced significantly fewer stress-related enzymes, compared to untreated mice. Viagra had no effect however on mice that lacked RGS2.