Blood volume is increased by the faster heart rate that can increase by 25% (normal 70 to 80-90 beats per minute). During pregnancy, the increased heart rate will increase cardiac output by 50-90% by the third trimester.
If the heart rate increases to greater than 100 beats per minute and especially associated with chest pain, shortness of breath, fainting or coughing up blood; a physician should be consulted to rule out serious health issues.
A common reason for diastolic dysfunction is the result of a non-compliant ventricular muscle wall that is stiff. A good example is muscle thickening (hypertrophy) resulting from aortic valve stenosis. In this case, the valve is scarred and does not open well causing the ventricular muscle to hypertrophy. The thickened muscle enables the ventricle to over come the resistance through the small valve opening but over time makes the ventricular stiff and noncompliant causing the ventricle to fill and empty inadequately. This resistance to blood flow across the valve can be auscultated with a stethoscope as a heart murmur.