Good Evening, Let me start by saying I am very sorry to hear about these symptoms your son is experiencing. Having said that, from personal experience these symptoms may or may not be separate from the heart murmur itself. Most diagnosed innocent heart murmurs are as their title suggests innocent. They can and most often will go on throughout an individuals life without causing any issue, except for that of a unique sound heard on physical exam. As for the symptoms you describe, these sound seperate but nevertheless certainly more serious. Very tired, pale stools, dark rings? It sounds to me like a systemic illness that requires complete workup with at a Complete Blood Count and Basic Metabolic Panel. These will let us know if he has an infection, if his blood is healthy and strong and sufficient, if there are any electrolytes and or nutrients out of balance, and or if particular organs and or tissues in the body are ill. Based on his symptoms, and age, I must admit there are a variety of potential causes; Viruses and infections such as Mono or the Flu typically can cause gastrointestinal and generalized effects such as those you describe. Nonetheless, as it can indeed just be a virus, even more benign than the Flu or Mono, it can also be a completely different entity entirely, and thus a formal test really needs to be done to hone in on exactly what that is. My suggestion is to make sure your son hydrates often and as soon as possible schedule a visit with a primary care physician. I would not rush him to the Emergency room unless a primary care physician could not be reached in an adequate period of time, or if your son starts to appear toxic and or the symptoms you are describing start to worsen. I truly hope for the best and believe you and your son will come out of this strong and well cared for. Warm Regards.