This could be a number of things; as there are an array of both rhythm and rate disorders and or abnormalities which cause the symptoms you describe. When you say your heart stops, be more specific? And when you say always suffered this, can you think of any things done before each episode, any activities you are engaging in at the time? Have you ever seen a cardiologist and been prescribed? If not; what do you do to improve the situation, and does anything work? Though I cannot provide to you diagnosis, I will say that there are a number of factors which can cause a fast heart rate. Caffeine, Amphetamines, Stress, a variety of medications; and then ultimately there are some inherent heart disorders where nothing is particularly causing it, and these must be ruled out. I would contact the physicians who ruled out your heart disorder and give them a call; explaining any changes in symptoms. If you ever start to feel chest pain, sweating, shortness of breath, and or lightheartedness with cardiac symptoms, call 911 and be taken to the Emergency Room.