A 45-year-old woman presents with sudden attacks of wheezing, shoness of breath, episodic hot flashes, abdominal cramps and diarrhea. Physical examination shows facial redness, as well as hepatomegaly and pitting edema of the lower legs. A 24-hour urine specimen reveals elevated levels of 5-hydroxyindoleacetic acid (5-HIAA). A CT scan of the abdomen demonstrates multiple 2- to 3-cm nodules throughout the liver and a 2-cm nodule in the jejunum. An echocardiogram would be most expected to demonstrate which of the following?