Is feeling the heart racing a common occurrence during pregnancy?

A significant number of cardiovascular changes occur during pregnancy, which may be accompanied by dyspnea and a reduced tolerance for endurance exercise. During pregnancy, women expand their blood volume by approximately 30-50%. This is accompanied by an increase in cardiac output. The heart rate may also increase by 10-20 beats per minute. The changes peak during weeks 20-24 and usually resolve completely within 6 weeks of childbirth.

The blood pressure in the upper extremities should change very little during pregnancy, but pressure in the lower extremities increases. This is accompanied by pedal edema. Because of extra blood flow, variances in the auscultated heart sounds may occur, such as murmurs, a wider split between the first and second heart sounds, or an S3 gallop. Some nonspecific ST-segment changes may occur, and some changes to the cardiac outline may appear on chest radiographs. The following is a summary of cardiovascular changes:

• Systolic blood pressure level decreases 4-6 mm Hg.
• Diastolic blood pressure level decreases 8-15 mm Hg.
• Mean blood pressure level decreases 6-10 mm Hg.
• Heart rate increases 12-18 beats per minute.
• Stroke volume increases 10-30%.
• Cardiac output increases 33-45%.

Source: http://emedicine.medscape.com/