There have been several high profile merger and acquisition deals that took place this past week. St. Jude has decided to buy Thoratec for $3.4B, Allergan has acquired NMDA depression drugs in a $560M-plus Naurex buyout, and Teva has inked a $40B-plus pact for Allergan’s generics biz. M&A deals are the quickest way for a company to expand and grow in the market.

St. Jude has announced its intention to acquire Thoratec for $3.4 billion, looking to incorporate its ventricular assist devices into St. Jude’s cardiology portfolio. St. Jude’s portfolio already includes pacemakers, cardiac imaging and remote monitoring. It will enter a high-growth market worth approximately $750 million a year. St. Jude is planning on pairing the heart pump with its CardioMEMs heart failure monitor. The deal is expected to close in Q4 2015.

Allergan has decided to purchase Naurex for $560 million. The buyout will give Allergan two high-profile antidepressants, the lead drug being GLYX-13. GLYX-13 is poised for a late stage study while a follow-up program is headed into a Phase IIb trial. Several developers, including J&J, have taken a shot at NMDA, but Naurex has separated itself from the rest with a lead therapy that has demonstrated quick action and a durable effect in a Phase IIb study.

Teva is going to give $40.5 billion, $33.75 billion in cash and shares valued at $6.75 billion, to Allergan. Allergan will have a 10% stake in Teva following the deal. In return, Teva will be included in a business that churned out $6.6 billion in sales last year, solidifying its position at the top of the generics food chain and moving it into the ranks of the world’s 10 largest drugmakers. Teva believes the deal will generate cost savings of about $1.4 billion annually, and the combined revenue could hit $26 billion.

M&A deals can have a really big effect on the market. St. Jude is spending $3.4 billion to acquire Thoratec, Allergan is spending $560 million to acquire Naurex, and Teva is spending $40.5 billion to share the generics business with Allergan. That is a lot of money exchanging hands, and it will be interesting to see what these companies do with the new products they have acquired.