I begin classes with reminders to be safe and comfortable in the practice of yoga. In the pursuit of yoga postures, it is common and valuable to feel the sensation of new or deeper movement. It is not valuable to push into pain. Understand your efforts, and release the goal that is unproductive.
Always avoid dizziness.
If you have cardiac issues including high blood pressure, take care in your physical activity. Modify your movements and poses so that your head stays above your heart.
I recommend a consultation with your doctor before beginning any new exercise.