The 70-year-old patient in the Auckland Hospital in New Zealand had suspiciously low blood pressure. The doctors were stumped. But they had an unusual experimental tool at their disposal: a unique computer program that analyzes a magnetic-resonance imaging (MRI) scan, measuring the motion of a patient's heart and comparing it to that of a "healthy" virtual heart constructed not of blood and tissue but from mathematical equations. The analysis handed the clinic's experts the smoking gun: part of the heart was twisting in a pattern often associated with a partially blocked valve, which, untreated, would probably kill the patient within three years.

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