When fabricating prototypes for an artificial heart valve, the process needs to carefully balance precision, material selection, and performance under simulated biological conditions. Here are the steps:

1. Material Selection
Biocompatibility: Choose materials like titanium, cobalt-chromium, or polymer composites. These materials are commonly used in medical devices for their strength and resistance to corrosion, ensuring that the valve will not cause adverse reactions in the body.
Durability: The material should withstand mechanical stresses over time. Polymeric materials or alloys that mimic the properties of natural heart tissue are often ideal.

2. Design and CAD Modeling
Use computer-aided design (CAD) software to create detailed 3D models of the valve, including its leaflets, housing, and mechanical components. Software like SolidWorks or AutoCAD is commonly used for precise modeling.
Consider the valve’s geometry, as the leaflet shape and the housing need to mimic the natural structure of heart valves for optimal functionality. Include channels for blood flow, the hinge mechanism, and sealing features.

3. Prototyping Techniques
3D Printing: For early-stage prototypes, 3D printing (using materials like SLA or SLS) is a popular method because it’s cost-effective and allows for rapid iteration. This can be used to create initial models for structural and flow testing.
Casting and Molding: Once a promising design is finalized, casting or molding techniques (e.g., silicone molding for soft tissue models) can be used to create functional prototypes. Metal valves can be fabricated using precision casting methods.
CNC Machining: For more refined prototypes, CNC machines can mill or carve components with high accuracy, especially for metallic or composite valves.

4. Assembly
After creating individual components (leaflets, housing, etc.), assemble the valve using tools for precise alignment and fitting. Pay special attention to the sealing mechanism and ensure there are no gaps that could lead to leakage or improper blood flow.

5. Functional Testing
Hemodynamic Testing: Set up a test rig to simulate the pressures and flows seen in the human circulatory system. This could involve using a pulse duplicator system that mimics blood flow patterns. This testing checks for functionality under real-world conditions.
Mechanical Testing: Assess the durability of the valve by applying cyclic loading to simulate heartbeats. This is typically done in a test chamber where the valve undergoes millions of open-close cycles under pressure.
Biocompatibility Testing: There's a need to test for biocompatibility if new materials are being used, to ensure that the material doesn’t cause adverse reactions when exposed to simulated biological conditions.

6. Iteration
After the first round of testing, there'll likely be a need to make adjustments to the design. The goal here is to address any weaknesses identified in the testing phase, whether it's improving blood flow dynamics or enhancing the valve’s mechanical robustness.

7. Finalization and Documentation
Once a functional prototype passes all necessary tests, document the design specifications, material choices, and performance results in detail. This documentation will be essential for regulatory approvals and further development steps.

By taking a methodical approach to prototyping—starting with accurate design, followed by rapid prototyping, testing, and refinement—it can be possible to ensure the artificial heart valve meets the functional and durability standards needed for clinical application.