Question: during valve replacement surgery a valve that comes from an animal is known as
[{'answer': 'Tissue heart valves', 'provenance': [{'wikipedia_id': '1114065', 'title': 'Aortic valve replacement', 'start_paragraph_id': 22, 'start_character': 0, 'end_paragraph_id': 22, 'end_character': 19, 'bleu_score': 1.0, 'section': 'Section::::Types of valves.:Tissue valves.\n'}]}]