Tissue engineered heart muscle may be able to provide a treatment modality for early stage congestive heart failure. In this study, we describe a new method to engineer functional 3-dimensional heart muscle utilizing a biodegradable fibrin gel. Primary cardiac myocytes were isolated from hearts of 2- to 3-day-old rats and processed in one of the two ways. For the first method (layering approach), the cells were plated directly on the surface of a fibrin gel-coated on polydimethylsiloxane (PDMS) surfaces. The cells were cultured in growth media and the contractile performance evaluated after formation of 3-dimensional tissue constructs. For the second method (embedding approach), the cells were suspended with thrombin and plated on 35 mm tissue culture surfaces coated with PDMS. Fibrinogen was then added to the surface. Within 7 days after initial cell plating, a 3-dimensional tissue construct of cells derived from primary heart tissue (termed bioengineered heart muscle, BEHM) resulted for both approaches. Histological evaluation showed the presence of uniformly distributed cardiac cells throughout the BEHM, both in longitudinal and cross sections. The stimulated active force of BEHMs formed using the layering approach was 835.5 +/- 57.2 muN (N = 6) and 145.3 +/- 44.9 muN (N = 6) using the embedding approach. The stimulated active force was dependent on the initial plating density. It was possible to maintain the contractile function of BEHM in culture for up to 2 months with daily medium changes. The BEHMs exhibited inotropy in response to external calcium and isoproterenol and could be electrically paced at frequencies of 1-7 Hz. We describe a novel method to engineer contractile 3-dimensional cardiac tissue construct with a fourfold increase specific force compared to our previous model.