When we exercise, more blood flow goes to our muscles, challenging our blood vessels. Following exercise, blood flow remains elevated and seems to be the reason for many of the positive cardiovascular benefits that occur with exercise. When the actions of histamine, a molecule primarily known for its role in allergies, are blocked, there is an attenuated blood flow response following exercise. However, this effect has never been studied in the blood vessels that supply our lungs. The purpose of this study is to examine the effects of histamines on pulmonary hemodynamics following exercise.

Inclusion Criteria:

1. Age: 19 - 39.
2. Willing to visit the lab on 3 separate occasions.

Exclusion Criteria:

1. Previously diagnosed heart condition,
2. Previously diagnosed lung condition (including asthma),
3. Previously diagnosed metabolic condition,
4. Currently smokers (cigarettes, electronic cigarettes, cannabis) or who have smoked within the last 3 months,
5. Resting blood pressure >140/90 mmHg,
6. Unable to obtain appropriate quality ultrasound images of the heart.,
7. Individuals without tricuspid regurgitation at rest to allow assessment of the primary outcome,
8. Pregnant or trying to become pregnant,
9. Breastfeeding,
10. Chronically take antihistamines (i.e. daily),
11. History of adverse reactions to antihistamines,
12. Never taken antihistamines previously,
13. Currently taking any medications (including oral contraceptives).