NitroMed ( NTMD) said Tuesday that Michael Loberg, its chief executive and president, and Lawrence Bloch, its chief financial officer, resigned effective immediately. Loberg also resigned as a director. The Lexington, Mass., drug company provided no reason for the executives' departure, which comes less than three weeks after NitroMed issued a dreadful fourth-quarter financial report . The company said sales of BiDil -- a treatment for congestive heart failure in African-Americans -- were disappointing. At the time, Loberg and Bloch attributed the weak sales to an inconsistent performance by its sales force and to high copayments charged by managed-care firms. They said they were reorganizing the sales force and stepping up discussions with insurers. The Food and Drug Administration approved BiDil in June as the first drug endorsed for a specific ethnic group. In July, NitroMed began marketing BiDil, which combines two generic drugs. NitroMed's stock had been sinking since August, losing about two-thirds of its value. But on Tuesday, shares gained 34 cents, or 3.1%, to $8.07 by midmorning. The stock climbed as high as $8.80. Loberg, 57, had been CEO and a director since September 1997. Bloch, 39, had been CFO since September 2004. NitroMed's board said Argeris Karabelas, 52, the company's chairman, has been appointed interim CEO. Karabelas also is a partner of Care Capital LLC, a life-sciences investment firm. Previously, he was CEO of worldwide pharmaceuticals at Novartis ( NVS). Karabelas has been NitroMed's chairman since August 2003. The board said Kenneth Bate will become CFO and chief operating officer. Bate has held executive positions with Millennium Pharmaceuticals ( MLNM) and with the former Biogen before it became Biogen Idec ( BIIB) through a merger.