Mast cells are a type of white blood cell found in connective tissue. They play a crucial role in the immune response and the inflammatory process. Mast cells are best known for their ability to release various chemical substances, including heparin and histamine.

1. Heparin:
- Heparin is an anticoagulant, which means it prevents blood clotting.
- It is produced and stored in mast cells within connective tissue.
- Heparin helps to inhibit the formation of blood clots, preventing them from becoming too large and potentially causing blockages in blood vessels.
- Its release from mast cells is especially important during an allergic reaction or inflammation when blood vessels may become damaged.

2. Histamine:
- Histamine is a compound that plays a critical role in the immune response and inflammation.
- It is released from mast cells in response to various triggers, such as allergens, pathogens, or injury.
- Histamine causes blood vessels to dilate, leading to increased blood flow to the affected area.
- It also increases vascular permeability, allowing immune cells and antibodies to reach the site of injury or infection more easily.
- Histamine is responsible for many of the symptoms associated with an allergic reaction, such as itching, redness, swelling, and increased mucus production.

3. Other Substances:
- Mast cells also contain other substances that they can release, including leukotrienes, prostaglandins, cytokines, and growth factors.
- These substances further contribute to the immune response and inflammation by attracting and activating other immune cells, promoting cell proliferation, and modulating the inflammatory process.

In conclusion, mast cells of connective tissue contain heparin and histamine. Heparin acts as an anticoagulant, preventing blood clotting, while histamine plays a crucial role in the immune response and inflammation. The release of these substances from mast cells helps to regulate and coordinate the body's response to injury, infection, or allergens.