Heart device maker Cardima Inc. raised $20 million in a private placement via a private placement memorandum offering. The Fremont business makes catheters used in diagnosing and treating heart problems like atrial fibrillation. Cardima sold 18.5 million shares at $1.08 each. The company plans to issue warrants for 5.55 million more shares of common stock at an exercise price of $1.25 to the buyer.