Is Treatment With Ritalin Safe In Children?

My 9 year old son was diagnosed as having ADHD and was prescribed Ritalin. He also has a heart murmur, allergies and asthma. He is taking the steroid Albuterol as an inhaler and breathing treatment. I have heard that Ritalin can cause more heart problems. Is it safe for him to be taking Ritalin or is there an alternative?