A 21-year-old woman is referred to cardiology clinic for evaluation. She was a passenger in a motor vehicle accident, and when she was evaluated in the emergency department, she was incidentally noted to have a loud heart murmur on exam and mild cardiomegaly on a chest radiograph. An ECG was obtained during her clinic visit and is shown in Fig. 157.1. Physical exam was notable for splitting of the first and second heart sounds and a holosystolic murmur at the left sternal border that increased with inspiration. The patient denied any history of chest pain or shortness of breath. She did report one previous episode of palpitations associated with near syncope. Her family history is notable for a cousin with a “heart rhythm problem.” What further testing does this patient require?