A 10-year-old girl experienced symptoms of leg weakness in both lower legs during the onset, unable to walk, with an increased heart rate and a slight fever of 38.2 degrees Celsius. She was conscious but without sweating. The symptoms lasted for 1-2 hours and then returned to normal. On the third day, she developed dizziness and loss of appetite. The cardiac ultrasound was normal, blood sugar levels were normal, and there was no potassium deficiency. What aspects should be considered in this situation?

A four-and-a-half-year-old child was found to have a heart murmur and irregular heartbeat during a medical check-up. The doctor recommended an echocardiogram to rule out congenital heart disease.