Abiomed and Thoratec are medical device companies. Abiomed's Impella is the world's smallest heart pump used for high-risk patients after surgery or heart attack. Thoratec's Heartmate II is a ventricular assist device for advanced heart failure. Both companies see growth opportunities in expanding their applications and markets. Thoratec has higher revenue growth, profitability, and valuation multiples, but also higher debt levels than the debt-free Abiomed, which has seen renewed optimism from recent sales growth of its Impella pump.